Positive electrode layer, method for producing the positive electrode layer, and all-solid-state battery

Abstract

To provide a positive electrode layer for an all-solid battery with low resistance.SOLUTION: A positive electrode layer used for an all-solid battery according to the present disclosure includes a positive electrode active material, and a coated sulfide solid electrolyte having a sulfide solid electrolyte and a coating layer covering the surface of the sulfide solid electrolyte and containing a metal sulfate, and in the S2p spectrum obtained by X-ray photoelectron spectroscopy (XPS) for the coated sulfide solid electrolyte, 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 more and less than 0.36.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a positive electrode layer, a method for manufacturing a positive electrode layer, and an all-solid-state battery. [Background technology]

[0002] An all-solid-state battery is a battery that has a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and has the advantage that it is easier to simplify safety devices compared to liquid batteries that have an electrolyte solution containing a flammable organic solvent.

[0003] In order to suppress an increase in the interface resistance between an active material and another material, a technique of forming a coating layer on the surface of an active material is known. For example, Patent Document 1 discloses an all-solid-state lithium secondary battery having a positive electrode layer containing a Li-containing sulfate-coated oxide-based positive electrode active material in which a Li-containing sulfate is formed on the surface of the oxide-based positive electrode active material, and a sulfide-based solid electrolyte material.

[0004] Patent Document 2 discloses a lithium metal oxide active material including a coating layer located on the surface of the active material, the coating layer being made of Li2S, Li2SO4, and Li2S n O x (n is 1≦n≦8)。 (n is 1≦n≦8) is one or more sulfur compounds selected from the group consisting of. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-080168 A [Patent Document 2] Patent Publication No. 2021-86834 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to increase the input / output of all-solid-state batteries, a positive electrode layer with low resistance is required. The present disclosure has been made in view of the above-mentioned problems, and has as its main object to provide a positive electrode layer with low resistance. [Means for solving the problem]

[0007] In order to solve the above problems, the present disclosure provides a positive electrode layer for use in an all-solid-state battery, the positive electrode layer comprising a positive electrode active material, a sulfide solid electrolyte, and a coated sulfide solid electrolyte having a coating layer that coats a surface of the sulfide solid electrolyte and contains a metal sulfate, wherein in an S2p spectrum obtained by X-ray photoelectron spectroscopy measurement (XPS) of the coated sulfide solid electrolyte, a ratio (P2 / P1) of a peak intensity P2 appearing in the vicinity of 167 eV to a peak intensity P1 appearing in the vicinity of 163 eV is 0.15 or more and less than 0.36.

[0008] According to the present disclosure, the positive electrode layer contains a predetermined coated sulfide solid electrolyte, thereby resulting in a positive electrode layer with low resistance.

[0009] In the above disclosure, it is preferable that the sulfide solid electrolyte contains Li, P and S, the peak appearing near 163 eV is derived from a PS bond, and the peak appearing near 167 eV is derived from an SO bond.

[0010] In the above disclosure, the metal sulfate is preferably lithium sulfate.

[0011] In the above disclosure, the surface of the positive electrode active material is provided with a compound having the general formula Li x AO y (A is at least one selected from the group consisting of Nb, B, Al, Si, P, S, Ti, Zr, Mo, Ta and W, and x and y are positive numbers).

[0012] The present disclosure also provides a method for producing a cathode layer used in an all-solid-state battery, the method including the steps of: obtaining a coated sulfide solid electrolyte by subjecting a sulfide solid electrolyte to a heat treatment at a temperature of 100° C. or higher and lower than 190° C. for 5 minutes to 1 hour in a dry gas to form a coating layer containing a metal sulfate on a surface of the sulfide solid electrolyte; and forming the cathode layer by applying and drying a slurry containing the coated sulfide solid electrolyte and a cathode active material.

[0013] According to the present disclosure, a positive electrode layer having low resistance can be manufactured by using a coated sulfide solid electrolyte obtained by heat treating a sulfide solid electrolyte in a dry gas at a predetermined temperature for a predetermined time.

[0014] The present disclosure also provides an all-solid-state battery having 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 above-mentioned positive electrode layer.

[0015] According to the present disclosure, by using the above-described positive electrode layer, an all-solid-state battery with low resistance is obtained. Effect of the Invention

[0016] The present disclosure has an effect of providing a positive electrode layer having low resistance. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a coated sulfide solid electrolyte according to the present disclosure. [Diagram 2] FIG. 2 is a flow diagram showing an example of a method for producing a positive electrode layer in the present disclosure. [Diagram 3] FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery according to the present disclosure. [Figure 4] 1 shows S2p ​​spectra obtained by XPS measurement of the coated sulfide solid electrolytes produced in Example 3 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The positive electrode layer, the method for producing the positive electrode layer, and the all-solid-state battery according to the present disclosure will be described in detail below.

[0019] A. Positive electrode layer The details of the positive electrode layer in the present disclosure will be described below. The positive electrode layer in the present disclosure includes a predetermined coated sulfide solid electrolyte and a positive electrode active material. FIG. 1 is a schematic cross-sectional view showing an example of the coated sulfide solid electrolyte in the present disclosure. The coated sulfide solid electrolyte 11 in the present disclosure has a sulfide solid electrolyte 11a and a coating layer 11b that coats the surface of the sulfide solid electrolyte 11a and contains a metal sulfate. Furthermore, in an S2p spectrum obtained by X-ray photoelectron spectroscopy measurement (XPS) for the coated sulfide solid electrolyte 11, the ratio (P2 / P1) of the intensity P2 of a peak appearing near 167 eV to the intensity P1 of a peak appearing near 163 eV is 0.15 or more and less than 0.36. Moreover, the positive electrode layer in the present disclosure is used in an all-solid-state battery.

[0020] According to the present disclosure, by including a predetermined coated sulfide solid electrolyte, a positive electrode layer having low resistance is obtained.

[0021] Conventionally, a coated positive electrode active material is known in which a coating layer containing lithium niobate (LiNbO3) is formed on the surface of a positive electrode active material. This coating layer has a function of suppressing the formation of a high resistance layer at the interface between the positive electrode active material and the sulfide solid electrolyte, thereby reducing the interface resistance when lithium ions move across the interface between the positive electrode active material and the sulfide solid electrolyte. On the other hand, when such a coated positive electrode active material is used, sulfur in the sulfide solid electrolyte and oxygen in the lithium niobate may react to form a resistance layer. For example, it is presumed that a side reaction represented by the following reaction formula occurs. LiNbO3+0.95Li3PS4→0.08Li5(NbS2)7+0.75Li3PO4+0.2Nb2PS 10 +0.59Li2S (Enthalpy change per mole of Li3PS4 (ΔH) = -160.9 kJ / mol)

[0022] Patent Document 1 also discloses an oxide-based positive electrode active material coated with a Li-containing sulfate, in which a Li-containing sulfate is formed on the surface of the positive electrode active material. When a Li-containing sulfate is formed on the surface of the positive electrode active material, the Li-containing sulfate may react with a sulfide electrolyte to form a resistance layer, as shown in the following reaction formula, for example. For example, it is presumed that a side reaction represented by the following reaction formula occurs. Li2SO4+0.89Li3PS4→0.89Li3PO4+0.44S8O+Li2S (Enthalpy change per mole of Li3PS4 (ΔH) = -166.3 kJ / mol)

[0023] In contrast, the present disclosure uses a coated sulfide solid electrolyte in which the surface of the sulfide solid electrolyte is coated in advance with a coating layer containing a metal sulfate. It is presumed that such a coated sulfide solid electrolyte changes the surface energy and the like due to the coating layer containing a metal sulfate being chemically bonded to the sulfide solid electrolyte, thereby suppressing the side reaction between the Li-containing sulfate and the sulfide solid electrolyte as described above. In addition, since the surface of the sulfide solid electrolyte is coated with a coating layer containing a metal sulfate, it is possible to suppress the generation of a high resistance layer caused by the reaction between the positive electrode active material and the sulfide solid electrolyte.

[0024] Furthermore, even when a positive electrode active material having a coating layer containing lithium niobate (LiNbO3) formed on the surface is used, the reaction between the metal sulfate in the coating layer of the coated sulfide solid electrolyte and the lithium niobate is unlikely to occur (there is no thermodynamically stable compound). Therefore, the formation of a high resistance layer can be suppressed.

[0025] 1. Coated sulfide solid electrolyte The coated sulfide solid electrolyte in the present disclosure has a sulfide solid electrolyte and a coating layer that coats the surface of the sulfide solid electrolyte and contains a metal sulfate.

[0026] In an S2p spectrum obtained by X-ray photoelectron spectroscopy (XPS) of the coated sulfide solid electrolyte, the ratio (P2 / P1) of the intensity P2 of a peak appearing near 167 eV to the intensity P1 of a peak appearing near 163 eV is 0.15 or more and less than 0.36. The P2 / P1 may be 0.18 or more, or 0.20 or more. On the other hand, the P2 / P1 may be 0.35 or less, or 0.30 or less.

[0027] The peak appearing near 163 eV is derived from PS bonds and appears, for example, at 159 eV to 163 eV, and the peak appearing near 167 eV is derived from SO bonds and appears, for example, at 165 eV to 175 eV. The larger the value of P2 / P1, the smaller the proportion of PS bonds and the larger the proportion of SO bonds on the surface of the coated sulfide solid electrolyte, which means that the formation of the coating layer has progressed.

[0028] According to the present 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 sufficiently formed, causing the sulfide solid electrolyte to react with the positive electrode active material, making it impossible to suppress the formation of a high resistance layer. Also, if the P2 / P1 ratio is too large, the battery resistance cannot be reduced. This is presumably because the coating layer is excessively formed, restricting the lithium ion path.

[0029] (1) Covering layer The coating layer in the present disclosure is formed on the surface of the sulfide solid electrolyte and contains a metal sulfate. Examples of metals contained in the metal sulfate include alkali metals such as Li and Na. As the metal sulfate in the present disclosure, a metal sulfate containing Li is preferable, and Li2SO4 is particularly preferable. This is because it has high Li conductivity. In addition, since Li2SO4 is a sulfate containing only Li as a metal element, other metal elements do not react with the positive electrode active material or the sulfide solid electrolyte. Therefore, the formation of a resistance layer due to such a reaction is suppressed, and the resistance to lithium ion conduction is reduced.

[0030] In addition, the thickness of the coating layer in the present disclosure is not particularly limited, but may be, for example, 1 nm or more, and may be 5 nm or more. On the other hand, it may be 20 nm or less, and may be 15 nm or less. This is because the resistance to lithium ion conduction can be reduced by making the thickness of the coating layer thinner. The thickness of the coating layer can be analyzed by adopting a method such as X-ray fluorescence analysis (XRF).

[0031] The coating layer in the present disclosure covers at least a portion of the surface of the sulfide solid electrolyte. The coating layer may be formed on a portion of the surface of the sulfide solid electrolyte, or on the entire surface. The coverage of the coating layer is, for example, 50% or more, 70% or more, or 90% or more.

[0032] It is presumed that the greater the amount of oxygen on the surface of the coated sulfide solid electrolyte in the present disclosure, the more the formation of the coating layer has progressed. The amount of oxygen (%) on the surface of the coated sulfide solid electrolyte is calculated by the following formula using the element concentration of each element obtained by XPS. Oxygen content (%) = (O element concentration / concentration of elements other than O element) x 100 The amount of oxygen (%) on the surface of the coated sulfide solid electrolyte is, for example, 5% or more, may be 20% or more, or may be 40% or more.

[0033] 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 by the following formula using the elemental concentrations of each element (O, S, P, Li, Br, and I) obtained by XPS. Oxygen content (%) = {O element concentration / (S+P+Li+Br+I) element concentration} x 100

[0034] (2) Sulfide solid electrolyte The sulfide solid electrolyte in the present disclosure usually contains sulfur (S) as a main component of an anion element. The sulfide solid electrolyte in the present disclosure preferably contains Li, P, and S. The sulfide solid electrolyte in the present disclosure may contain only Li, P, and S, or may contain other elements. Examples of other elements include X (X is a halogen element). Examples of X include F, Cl, Br, and I. X may be one type, or two or more types. Among them, the sulfide solid electrolyte preferably further contains at least one of Br and I.

[0035] In addition, the sulfide solid electrolyte of the present disclosure preferably includes an ion conductor containing Li, P, and S. The ion conductor has an anion structure with an ortho composition (PS4 3- ) as the main component of the anion. This is because it has high chemical stability. The ratio of the anion structure with the ortho composition to the total anion structures in the ionic conductor is, for example, 70 mol % or more, or may be 80 mol % or more, or may be 90 mol % or more. The ratio of the anion structure with the ortho composition can be determined, for example, by Raman spectroscopy, NMR, or XPS.

[0036] The sulfide solid electrolyte may contain a lithium halide in addition to the ion conductor. Examples of the lithium halide include LiF, LiCl, LiBr, and LiI, and among them, LiCl, LiBr, and LiI are 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 LiX is, for example, 30 mol% or less, and may be 25 mol% or less.

[0037] 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 be greater than 0. In this case, x may be 5 or more, and may be 10 or more. Also, x may be 50 or less, and may be 30 or less. Also, y may be greater than 0. In this case, y may be 5 or more, and may be 10 or more. Also, y may be 50 or less, and may be 30 or less. z may be 50 or more, and may be 60 or more. α may be 0.72 or more, and may be 0.74 or more. On the other hand, α may be 0.78 or less, and may be 0.76 or less.

[0038] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte, may be a glass-ceramic-based sulfide solid electrolyte, or may be a crystalline sulfide solid electrolyte.

[0039] Examples of the shape of the sulfide solid electrolyte include particulate form. The average particle diameter (D50) of the sulfide solid electrolyte is, for example, 0.1 μm or more, and may 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 be 30 μm or less. The average particle diameter (D50) can be determined, for example, by observation using a scanning electron microscope (SEM). It is preferable that the number of samples is large, for example, 100 or more. Also, it is preferable that the sulfide solid electrolyte has 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 be 1×10 -3 S / cm or more.

[0040] (3) Coated sulfide solid electrolyte 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 be 10% by weight or more and 60% by weight or less. If the proportion of the coated sulfide solid electrolyte is low, there is a possibility that the ion conduction path is not sufficiently formed. On the other hand, if the proportion of the coated sulfide solid electrolyte is high, there is a possibility that the volumetric energy density is low.

[0041] The positive electrode layer in the present disclosure may contain only the coated sulfide solid electrolyte as the solid electrolyte, or may contain other solid electrolytes. The total ratio of the coated sulfide solid electrolytes to all the solid electrolytes contained in the positive electrode layer is, for example, 50% by weight or more, 70% by weight or more, or 90% by weight or more.

[0042] The method for producing the coated sulfide solid electrolyte is not particularly limited as long as the above-mentioned coated sulfide solid electrolyte can be obtained. For example, the method described below in "B. Method for producing positive electrode layer: 1. Coated sulfide solid electrolyte production step" can be used.

[0043] The coated sulfide solid electrolyte of the present disclosure can also be produced by subjecting the sulfide solid electrolyte to an oxygen plasma treatment, in which the oxygen plasma conditions are adjusted so that the P2 / P1 of the S2p spectrum obtained by XPS for the coated sulfide solid electrolyte falls within a predetermined range.

[0044] 2.Cathode active material The positive electrode layer in the present disclosure has a positive electrode active material. An example of the positive electrode active material in the present disclosure is an oxide active material. The oxide active material is particularly likely to form a high resistance layer between the oxide active material and the sulfide solid electrolyte. Examples of the oxide active material include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5)O4, olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, ramsdellite type active materials such as Li2Ti3O7, and solid solution type active materials including Li2MnO3.

[0045] The oxide active material is, for example, a material represented by the general formula Li x M y O z (M is a metal element other than Li, and x=0.02 to 2.2, y=1 to 2, and z=1.4 to 4). In the above general formula, M is preferably at least one selected from the group consisting of Co, Al, Mn, Ni, V, Fe, and Si, and more preferably at least one selected from the group consisting of Co, Ni, Al, and Mn.

[0046] Among them, the oxide active material is preferably lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), or lithium nickel oxide.

[0047] It is preferable that a coating layer containing an ion-conductive oxide is formed on the surface of the positive electrode active material in the present disclosure. The Li ion-conductive oxide is not particularly limited, but for example, the Li ion-conductive oxide represented by the general formula Li x AO y (A is at least one selected from the group consisting of Nb, B, Al, Si, P, S, Ti, Zr, Mo, Ta, and W, and x and y are positive numbers.) Specific examples include LiNbO3, Li3BO3, LiBO2, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 , Li2Ti2O5, Li2ZrO3, Li2MoO4, Li2WO4, etc. The Li ion conductive oxide may be a composite compound of Li ion conductive oxides. Among them, LiNbO3 is preferable.

[0048] The thickness of the coating layer is preferably within a range of, for example, 0.1 nm to 100 nm, and more preferably within a range of 1 nm to 20 nm. If the coating layer is too thick, the Li ion conductivity and the electronic conductivity may be reduced. The thickness of the coating layer can be measured, for example, by X-ray fluorescence analysis (XRF) or a transmission electron microscope (TEM).

[0049] In addition, the coverage of the coating layer on the surface of the positive electrode active material is preferably high, specifically, preferably 50% or more, more preferably 80% or more. The coating layer may cover the entire surface of the positive electrode active material. The method for measuring the coverage of the coating layer may include, for example, X-ray photoelectron spectroscopy (XPS). For example, when a coating layer containing lithium niobate (LiNbO3) is formed on the surface of lithium nickel cobalt manganese oxide (NCM) which is a positive electrode active material, the number of moles of Ni, Co, Mn, and Nb on the surface of the positive electrode active material is measured by XPS, and the number of moles of Nb can be calculated from the molar fraction of Nb relative to the total number of moles of Ni, Co, Mn, and Nb.

[0050] The proportion of the positive electrode active material in the positive electrode layer is, for example, 20% by weight or more, or may be 30% by weight or more, or may be 40% by weight or more, while the proportion of the positive electrode active material is, for example, 90% by weight or less, or may be 85% by weight or less, or may be 80% by weight or less.

[0051] 3. Positive electrode layer The positive electrode layer in the present disclosure contains the above-mentioned coated sulfide solid electrolyte and positive electrode active material, and may further contain at least one of a conductive material and a binder, if necessary.

[0052] Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). 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, and may be 0.3% by weight or more and 10% by weight or less.

[0053] Examples of the binder include rubber-based binders and fluoride-based binders. The content of the binder in the positive electrode layer is, for example, 0.1% by weight to 30% by weight, and may be 0.1% by weight to 15% by weight.

[0054] The thickness of the positive electrode layer is, for example, not less than 0.1 μm and not more than 1000 μm.

[0055] B. Method of manufacturing the positive electrode layer Fig. 2 is a flow diagram showing an example of a method for producing a positive electrode layer in the present disclosure. In the production method shown in Fig. 2, first, a sulfide solid electrolyte is heat-treated in dry gas at a temperature of 100°C or higher and lower than 190°C for 5 minutes to 1 hour to form a coating layer containing a metal sulfate on the surface of the sulfide solid electrolyte, thereby obtaining a coated sulfide solid electrolyte (coated sulfide solid electrolyte preparation step). Next, a slurry containing the coated sulfide solid electrolyte and a positive electrode active material is applied and dried to form a positive electrode layer (positive electrode layer formation step).

[0056] According to the present disclosure, a positive electrode layer for an all-solid-state battery having low resistance can be manufactured. Hereinafter, the method for manufacturing the positive electrode layer according to the present disclosure will be described step by step.

[0057] 1. Preparation of coated sulfide solid electrolyte The sulfide solid electrolyte used in this step is the same as the sulfide solid electrolyte described in "A. Positive electrode layer 1. Coated sulfide solid electrolyte (2) Sulfide solid electrolyte" above, and therefore a description thereof will be omitted here.

[0058] The dry gas is a gas having a low dew point with a dew point temperature of 0° C. or less. The dew point temperature may be, for example, −50° C. or less, or −60° C. or less. The oxygen concentration in the dry gas is, for example, 20% by volume or less. The dry gas is, for example, dry air.

[0059] The heat treatment in dry gas can be performed, for example, by using a hot plate or the like in a dry gas glove box.

[0060] The heat treatment temperature in the dry gas is usually 100°C or higher, may be 120°C or higher, or may be 130°C or higher. If the heat treatment temperature is too low, the coating layer is not sufficiently formed, and the formation of the high resistance layer cannot be suppressed. On the other hand, the heat treatment temperature is usually lower than 190°C, and may be 180°C or lower, or may be 170°C or lower. If the heat treatment temperature is too high, the coating layer is excessively formed, and the lithium ion path may be restricted.

[0061] The heat treatment time in the dry gas is usually from 5 minutes to 1 hour.

[0062] The coated sulfide solid electrolyte produced by this process is the same as that described above in "A. Positive electrode layer 1. Coated sulfide solid electrolyte", and therefore will not be described here. According to this process, a coated sulfide solid electrolyte is usually produced in which the coating layer contains lithium sulfate.

[0063] 2. Positive electrode layer formation process This step is a step of forming a positive electrode layer by applying a slurry containing a coated sulfide solid electrolyte and a positive electrode active material and drying it. The slurry may further contain a binder, a conductive material, and a solvent as necessary. The solvent has a broad meaning including a dispersion medium.

[0064] The above-mentioned slurry is preferably applied onto a current collector. The method of applying the slurry is not particularly limited, and any known application method can be adopted. The positive electrode layer produced by each of the above-mentioned steps is the same as that described in "A. Positive electrode layer" above, and therefore the description here is omitted.

[0065] C. All-solid-state battery Fig. 3 is a schematic cross-sectional view illustrating an all-solid-state battery according to the present disclosure. The all-solid-state battery 10 shown in Fig. 3 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 electrode current collector 4 that collects current from the positive electrode layer 1, and a negative electrode current collector 5 that collects current from the negative electrode layer 2. In the present disclosure, the positive electrode layer 1 is the positive electrode layer described above in "A. Positive electrode layer".

[0066] According to the present disclosure, by using the above-described positive electrode layer, an all-solid-state battery with low resistance is obtained.

[0067] 1. Positive electrode layer The positive electrode layer in this disclosure is similar to the content described above in "A. Positive electrode layer," and therefore will not be described here.

[0068] 2. Negative electrode layer The negative electrode layer in the present disclosure is a layer containing at least a negative electrode active material. The negative electrode active material layer may contain at least one of a solid electrolyte, a conductive material, and a binder, as necessary.

[0069] The negative electrode active material is not particularly limited, but examples thereof include metal active materials, carbon active materials, and oxide active materials. Examples of the metal active material include simple metals and metal alloys. Examples of the metal elements contained in the metal active material include Si, Sn, In, and Al. The metal alloy is preferably an alloy containing the above metal elements as a main component.

[0070] On the other hand, examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of the oxide active material include Li4Ti5O 12 Lithium titanates such as those mentioned above are also included.

[0071] The proportion of the negative electrode active material in the negative electrode layer is, for example, 20% by weight or more, or may be 30% by weight or more, or may be 40% by weight or more, while the proportion of the negative electrode active material is, for example, 80% by weight or less, or may be 70% by weight or less, or may be 60% by weight or less.

[0072] The solid electrolyte is the same as that described in "3. Solid electrolyte layer" below, and therefore the description thereof will be omitted here.

[0073] The conductive material and the binder are the same as those described in "A. Positive electrode layer" above, and therefore the description thereof will be omitted here. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0074] 3.Solid electrolyte layer The solid electrolyte layer in the present 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.

[0075] The solid electrolyte may be a conventionally known solid electrolyte that is generally used in all-solid-state lithium ion batteries, such as a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, a halide, etc., and among these, a sulfide solid electrolyte is preferable. The sulfide solid electrolyte is the same as that described in "A. Positive electrode layer" above, and therefore will not be described here.

[0076] The binder is the same as that described in “A. Positive electrode layer”, and therefore the description here is omitted. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0077] 4.All-solid-state battery In the present disclosure, the term "all-solid-state battery" refers to a battery having a solid electrolyte layer (at least a layer containing a solid electrolyte). In addition, the all-solid-state battery in the present disclosure has at least one power generating element having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and may have two or more. When the all-solid-state battery has a plurality of power generating elements, they may be connected in parallel or in series. The power generating element usually has a positive electrode current collector and a negative electrode current collector. The positive electrode current collector is disposed, for example, on the surface of the positive electrode layer opposite to the solid electrolyte layer. Examples of the material for the positive electrode current collector include metals such as aluminum, SUS, and nickel. Examples of the shape of the positive electrode current collector include a foil shape and a mesh shape. In addition, a carbon coat layer may be formed on the surface of the positive electrode current collector on the positive electrode layer side. On the other hand, the negative electrode current collector is disposed, for example, on the surface of the negative electrode layer opposite to the solid electrolyte layer. Examples of the material for the negative electrode current collector include metals such as copper, SUS, and nickel. Examples of the shape of the negative electrode current collector include a foil shape and a mesh shape.

[0078] The all-solid-state battery in the present disclosure may include an exterior body that houses the power generating element. Examples of the exterior body include a laminate-type exterior body and a case-type exterior body. The all-solid-state battery in the present disclosure may also include a restraining jig that applies a restraining pressure in the thickness direction to the power generating element. A known jig can be used as the restraining jig. The restraining pressure may be, for example, 0.1 MPa or more and 50 MPa or less, and may be 1 MPa or more and 20 MPa or less. If the restraining pressure is small, there is a possibility that a good ion conductive path and a good electron conductive path will not be formed. On the other hand, if the restraining pressure is large, the restraining jig may become large, and the volumetric energy density may decrease.

[0079] The type of all-solid-state battery in the present disclosure is not particularly limited, but is typically a lithium-ion secondary battery. The use of the all-solid-state battery is not particularly limited, but examples thereof include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, it is preferable to use the all-solid-state battery as a driving power source for hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. In addition, the all-solid-state battery in the present disclosure may be used as a power source for moving bodies other than vehicles (for example, railways, ships, and aircraft), and may be used as a power source for electrical products such as information processing devices.

[0080] The present disclosure is not limited to the above-described embodiment. The above-described embodiment is merely an example, and any configuration that is substantially the same as the technical idea described in the claims of the present disclosure and that exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

[0081] [Example 1] (Preparation of negative electrode structure) Anode active material (Si particles, average particle size 0.5μm), sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5)(mol%), average particle size 0.5μm), conductive material (VGCF-H), and binder (SBR) were prepared. These were weighed out so that the weight ratio of anode active material:sulfide solid electrolyte:conductive material:binder was 47.0:44.6:7.0:1.4, and mixed with a dispersion medium (diisobutyl ketone). The mixture was dispersed with an ultrasonic homogenizer (UH50, manufactured by SMT Co., Ltd.) to obtain anode slurry. The obtained anode slurry was applied to anode current collector (Ni foil, thickness 22μm) by a blade coat method using an applicator, and dried at 100℃ for 30 minutes. Thereafter, the opposite surface of the negative electrode current collector was similarly coated to obtain a double-sided negative electrode structure having a negative electrode layer and a negative electrode current collector. The thickness of the negative electrode layer on one side was 60 μm.

[0082] (Preparation of coated sulfide solid electrolyte) 2 g of sulfide solid electrolyte (10LiI 15LiBr 75(0.75Li2S 0.25P2S5) (mol%), average particle size 0.5μm) was heated at 100℃ for 5 minutes using a hot plate in a dry air atmosphere with a dew point of -70℃ and an oxygen volume concentration of 20%. As a result, a coating layer containing lithium sulfate was formed on the surface of the sulfide solid electrolyte, and a coated sulfide solid electrolyte was obtained.

[0083] (Preparation of positive electrode member) Positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 O2, average particle size 10 μm), the coated sulfide solid electrolyte obtained above, a conductive material (VGCF-H), and a binder (SBR) were prepared. These were weighed out so that the weight ratio of the 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 obtained mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a positive electrode slurry. The obtained positive electrode slurry was applied on an Al foil (thickness 15 μm) by a blade coating method using an applicator, and dried at 100 ° C for 30 minutes. As a result, a positive electrode member having a positive electrode layer and an Al foil was obtained. The thickness of the positive electrode layer was 100 μm.

[0084] (Preparation of solid electrolyte layer components) A sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 2.0μm) and a binder (SBR) were weighed out so that the weight ratio of sulfide solid electrolyte:binder was 99.6:0.4. These were mixed with a dispersion medium (diisobutyl ketone). The mixture obtained was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a slurry for a solid electrolyte layer. The obtained slurry for a solid electrolyte layer was applied to an Al foil (thickness 15μm) by a blade coating method using an applicator, and dried at 100°C for 30 minutes. As a result, a solid electrolyte layer member having an Al foil and a solid electrolyte layer was obtained. The thickness of the solid electrolyte layer was 30μm.

[0085] (Production of all-solid-state batteries) The negative electrode structure and the solid electrolyte layer member were cut to a size of 7.2 cm x 7.2 cm, while the positive electrode member was cut to a size of 7.0 cm x 7.0 cm. The solid electrolyte layer of the solid electrolyte layer member was brought into contact with the negative electrode layer located on one surface side of the negative electrode structure, and the solid electrolyte layer of the solid electrolyte layer member was also brought into contact with the negative electrode layer located on the other surface side of the negative electrode structure. The obtained laminate was pressed at a linear pressure of 1.6 t / cm by a roll press method. Next, the Al foil was peeled off from each solid electrolyte layer to expose the solid electrolyte layer. Then, the exposed solid electrolyte layer was attached to the positive electrode layer of the positive electrode member so as to be in direct contact with each other. The obtained laminate was pressed at a linear pressure of 1.6 t / cm by a roll press method. Next, the Al foil was peeled off from each positive electrode active material layer to expose the positive electrode active material layer, and further pressed at a linear pressure of 5 t / cm by a roll press method. Next, a positive electrode current collector (Al foil, thickness 15 μm) was placed on each of the roll-pressed positive electrode active material layers. Next, current collecting tabs were attached to the positive electrode current collector and the negative electrode current collector, respectively, and laminated and sealed to obtain an all-solid-state battery.

[0086] [Examples 2 to 4 and Comparative Example 4] 2 g of sulfide solid electrolyte (10LiI 15LiBr 75(0.75Li2S 0.25P2S5) (mol%), average particle size 0.5μm) was heated on a hot plate in a dry air atmosphere with a dew point of -70℃ and an oxygen volume concentration of 20% under the temperature and time conditions shown in Table 1. As a result, a coated sulfide solid electrolyte was obtained. An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained coated sulfide solid electrolyte was used.

[0087] [Comparative Example 1 and Comparative Example 3] A sulfide solid electrolyte (10LiI 15LiBr 75(0.75Li2S 0.25P2S5) (mol%), average particle size 0.5μm) was placed in dry air at room temperature for the time shown in Table 1 to obtain a coated sulfide solid electrolyte. An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained coated sulfide solid electrolyte was used.

[0088] [Comparative Example 2] An all-solid-state battery was fabricated in the same manner as in Example 1, except that the sulfide solid electrolyte (10LiI 15LiBr 75(0.75Li2S 0.25P2S5) (mol %), average particle size 0.5 μm) was used as is without being subjected to a heat treatment in dry air.

[0089] (XPS measurement) X-ray photoelectron spectroscopy (XPS) was performed on the coated sulfide solid electrolytes produced in Examples 1 to 4 and Comparative Examples 1 to 4. The ratio (P2 / P1) of the intensity P2 of the peak appearing near 167 eV to the intensity P1 of the peak appearing near 163 eV in the S2p spectrum is shown in Table 1. The peak appearing near 163 eV is derived from the PS bond, and the peak appearing near 167 eV is derived from the SO bond. FIG. 4 shows the S2p spectra obtained by XPS measurement on the coated sulfide solid electrolytes produced in Example 3 and Comparative Example 1.

[0090] The oxygen content (%) on the surface of the coated sulfide solid electrolytes produced in Examples 1 to 4 and Comparative Examples 1 to 4 was calculated by the following formula using the element concentration of each element (O, S, P, Li, Br, and I) obtained by XPS. The relative values ​​of the oxygen content in Examples 1 to 4 and Comparative Examples 2 to 4, assuming the oxygen content in Comparative Example 1 to be 1, are shown in Table 1. Oxygen content (%) = O / (S+P+Li+Br+I)

[0091] (Charge / discharge test) The all-solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were fixed-size constrained under a constraining pressure of 5 MPa, and were charged at 0.0194 A at a constant current-constant voltage (CC-CV) up to 4.05 V. Then, CC-CV discharge was performed at 0.0194 A up to 3.0 V. Then, the all-solid-state batteries were charged again. This charge was regarded as the initial charge. The resistance from the start of discharge (0 seconds) to 0.1 seconds was calculated from the voltage drop from the start of the initial discharge at 0.1 seconds. The results are shown in the "initial 0.1s resistance" column in Table 1. Furthermore, the resistance from 0.1 seconds to 10 seconds was calculated from the voltage drop from 0.1 seconds to 10 seconds. The results are shown in the "initial 10s resistance" column in Table 1. It is considered that the "initial 0.1s resistance" is correlated with the interface resistance between the positive electrode active material and the sulfide solid electrolyte. The "initial 10s resistance" is thought to be correlated with the ion conduction resistance in the positive electrode layer.

[0092] (Evaluation of reaction resistance during high cycles) The all-solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were restrained to a fixed size at a restraining pressure of 5 MPa, and were charged at 0.461 mA by constant current-constant voltage (CC-CV) to 4.35 V. Then, CC-CV discharge was performed at 0.461 mA to 3.0 V. Then, the all-solid-state batteries were charged again. This charge was regarded as the initial charge. Evaluation was performed up to 100 cycles at 2C.

[0093] The internal resistance was evaluated by the impedance method. Specifically, after the first charge and discharge, the SOC was adjusted to 40% and the impedance hole component value was obtained. Similarly, the internal resistance was evaluated after 100 cycles. The resistance increase rate (times) was calculated using the following formula. The results are shown in Table 1. Resistance increase rate (times) = internal resistance after 100 cycles ÷ internal resistance after 1 cycle

[0094] [Table 1]

[0095] From the results in Table 1, it was confirmed that the all-solid-state batteries of Examples 1 to 4 had lower resistance than the all-solid-state batteries of Comparative Examples 1 to 4. [Explanation of symbols]

[0096] 1 ... Positive electrode layer 2 ... Negative electrode layer 3...Solid electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...All-solid-state battery 11...Coated sulfide solid electrolyte 11a...Sulfide solid electrolyte 11b…Covering layer

Claims

1. A positive electrode layer for use in an all-solid-state battery, A positive electrode active material; A sulfide solid electrolyte; and a coated sulfide solid electrolyte having a coating layer containing a metal sulfate and coating a surface of the sulfide solid electrolyte, In an S2p spectrum obtained by X-ray photoelectron spectroscopy (XPS) of the coated sulfide solid electrolyte, the ratio (P2 / P1) of the intensity P2 of a peak appearing near 167 eV to the intensity P1 of a peak appearing near 163 eV is 0.15 or more and less than 0.36; The sulfide solid electrolyte contains Li, P and S, The peak appearing near 163 eV is due to a P-S bond, The peak appearing near 167 eV is derived from an S—O bond.

2. The positive electrode layer of claim 1 , wherein the metal sulfate is lithium sulfate.

3. The surface of the positive electrode active material is provided with a compound represented by the general formula Li ｘ A.O. ｙ (A is at least one selected from the group consisting of Nb, B, Al, Si, P, S, Ti, Zr, Mo, Ta, and W, and x and y are positive numbers).

4. A method for producing a positive electrode layer for use in an all-solid-state battery, comprising the steps of: a step of subjecting a sulfide solid electrolyte to a heat treatment in a dry gas at a temperature of 100° C. or more and less than 190° C. for 5 minutes to 1 hour to form a coating layer containing a metal sulfate on a surface of the sulfide solid electrolyte, thereby obtaining a coated sulfide solid electrolyte; and applying and drying a slurry containing the coated sulfide solid electrolyte and a positive electrode active material to form the positive electrode layer.

5. An all-solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, An all-solid-state battery, wherein the positive electrode layer is the positive electrode layer according to any one of claims 1 to 3.

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