Solid electrolyte, active material, electrode mixture, solid electrolyte layer, and solid-state battery

Abstract

The present invention addresses the problem of providing a solid-state battery and active material capable of suppressing decreases in the recovery capacity of the solid-state battery and capable of suppressing increases in the resistance of the solid-state battery, even if the solid-state battery is stored in a high-temperature environment in a charged state. A solid electrolyte, according to the present invention, contains a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element, an oxygen (O) element, and a halogen (X) element. The molar ratio of the halogen (X) element to the phosphorus (P) element is less than 1.2. The molar ratio of the oxygen (O) element to the phosphorus (P) element is greater than 0.001 but less than 1.0. According to the present invention, the X-ray diffraction pattern measured by an X-ray diffractometer using Cu Kα radiation has diffraction peaks at a position of 2θ=15.4°±1° and at a position of 2θ=17.8°±1°.

Description

Solid electrolyte, active material, electrode mixture, solid electrolyte layer and solid battery

[0001] The present invention relates to a solid electrolyte and an active material. The present invention also relates to an electrode mixture, a solid electrolyte layer, and a solid-state battery containing the solid electrolyte or the active material.

[0002] In recent years, secondary batteries have been attracting attention as an effort to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries using sulfide solid electrolytes have attracted attention. Solid-state batteries using sulfide solid electrolytes have the advantage of simplifying safety devices and achieving excellent manufacturing costs and productivity because they do not use flammable organic solvents. Furthermore, this type of solid electrolyte is advantageous from the perspective of improving safety and durability, since ionic species other than lithium ions do not migrate within the electrolyte, preventing side reactions due to the migration of anions.

[0003] With the aim of improving the performance of solid-state batteries, the present applicant previously proposed a solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (Ha), and including a crystalline phase with an argyrodite-type crystal structure (see Patent Document 1). In this solid electrolyte, the molar ratio of halogen (Ha) to phosphorus (P) is greater than 1.0 and less than 2.4, and the molar ratio of oxygen (O) to phosphorus (P) is greater than 0 and less than 0.5. This solid electrolyte has the advantage of being able to maintain lithium ion conductivity while achieving excellent battery characteristics when used in a solid-state battery.

[0004] US2023 / 231183A1

[0005] As a result of intensive research by the present inventors to further improve the performance of solid-state batteries, they have discovered a new problem: during storage of a solid-state battery, particularly during storage in a charged state in a high-temperature environment, a reaction occurs between the solid electrolyte and the active material, resulting in a deterioration in the performance of the solid-state battery. In other words, an object of the present invention is to suppress the reaction between the solid electrolyte and the active material during storage of a solid-state battery.

[0006] The present invention provides a solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and a halogen (X), wherein the molar ratio of the halogen (X) to the phosphorus (P) is less than 1.2, and the molar ratio of the oxygen (O) to the phosphorus (P) is greater than 0.001 and less than 1.0, and wherein the solid electrolyte has diffraction peaks at 2θ=15.4°±1° and 2θ=17.8°±1° in an X-ray diffraction pattern measured with an X-ray diffractometer using CuKα radiation.

[0007] The present invention also provides an active material comprising a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the coating layer contains a solid electrolyte including a crystalline phase having an argyrodite-type crystal structure, and the solid electrolyte contains lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and a halogen (X), and the molar ratio of oxygen (O) to phosphorus (P) is greater than 0.001 and less than 1.0.

[0008] FIG. 1 is an X-ray diffraction chart of the solid electrolytes obtained in the examples and comparative examples.

[0009] The present invention will be described below based on preferred embodiments. The present invention relates to a solid electrolyte and an active material having a coating layer of the solid electrolyte. The solid electrolyte and active material of the present invention will be described below.

[0010] [Solid Electrolyte] The solid electrolyte of the present invention preferably has lithium ion conductivity. The solid electrolyte is particularly preferably a sulfide solid electrolyte. The sulfide solid electrolyte preferably contains lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and a halogen (X). Examples of the halogen (X) element include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The X element may be one of these elements, or a combination of two or more of them. In particular, the X element preferably includes at least one of Cl and Br, and is preferably a combination of Cl and Br.

[0011] The solid electrolyte of the present invention may be crystalline or amorphous, but is preferably a crystalline substance. The solid electrolyte of the present invention preferably exhibits a diffraction peak at a specific angle in a diffraction pattern obtained by subjecting the solid electrolyte to X-ray diffraction. The solid electrolyte of the present invention exhibiting a diffraction peak at a specific angle is less likely to react with the active material, even when a solid battery containing the solid electrolyte is stored at high temperatures in a charged state or when the operating environment of the solid battery becomes unintentionally severe, for example, when the temperature rises. This suppresses a decrease in the recovery capacity of the solid battery and an increase in the resistance of the solid battery.

[0012] Specifically, in the X-ray diffraction pattern of the solid electrolyte of the present invention measured by an X-ray diffractometer, a diffraction peak A is preferably observed at 2θ = 15.4° ± 1°, and a diffraction peak B is preferably observed at 2θ = 17.8° ± 1°. The ranges of the diffraction peaks A and B are each independently preferably ±0.7°, more preferably ±0.5°, and particularly preferably ±0.3°. When obtaining the X-ray diffraction pattern, Cu-Kα is used as the radiation source. Hereinafter, in all references to X-ray diffraction patterns in this specification, Cu-Kα is used as the radiation source.

[0013] In the solid electrolyte of the present invention, in addition to the diffraction peaks being observed at the angles described above, it is preferable that the intensity ratio of the two diffraction peaks has a specific relationship. This makes it difficult for a solid battery containing the solid electrolyte of the present invention to react with the active material, even when the battery is stored at a high temperature in a charged state or when the operating environment of the solid battery becomes unintentionally severe, for example, when the temperature rises, and thereby further advantageously suppresses a decrease in the recovery capacity of the solid battery and an increase in the resistance of the solid battery. In particular, the integrated intensity of the diffraction peak A is expressed as I Ａ and the integrated intensity of the diffraction peak B is I Ｂ When I Ａ / I Ｂ The value of I is preferably 0.70 or more, more preferably 1.0 or more, and even more preferably 1.3 or more. Ａ / I Ｂ The value is preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

[0014] In the solid electrolyte of the present invention, in addition to diffraction peaks A and B, diffraction peak C is preferably observed at 2θ = 25.3° ± 1°, and diffraction peak D is preferably observed at 2θ = 29.7° ± 1°. The ranges of diffraction peaks C and D are each independently preferably ± 0.7°, more preferably ± 0.5°, and particularly preferably ± 0.3°.

[0015] In the solid electrolyte of the present invention, in addition to the diffraction peaks C and D being observed, it is preferable that the intensity ratio of the two diffraction peaks has a specific relationship. This makes it difficult for a solid battery containing the solid electrolyte of the present invention to react with the active material, even when the battery is stored in a charged state at high temperature or when the operating environment of the solid battery becomes unintentionally severe, for example, when the temperature becomes high, thereby further achieving the advantageous effects of suppressing a decrease in the recovery capacity of the solid battery and suppressing an increase in the resistance of the solid battery. In particular, in the solid electrolyte of the present invention, the integrated intensity of the diffraction peak C is set to I Ｃ and the integrated intensity of the diffraction peak D is IＤ When I Ｃ / I Ｄ The value of I is preferably 0.91 or less, and more preferably 0.90 or less. Ｃ / I Ｄ The value of is preferably 0.60 or more, more preferably 0.75 or more, and even more preferably 0.85 or more.

[0016] As described above, the solid electrolyte of the present invention is preferably a crystalline substance, and in particular, the solid electrolyte preferably has an argyrodite-type crystal structure because it has excellent lithium ion conductivity. When the solid electrolyte of the present invention has a crystalline phase with an argyrodite-type crystal structure, the solid electrolyte has a composition formula (I): Li ａ P.S. ｂ O ｃ X ｄ (X is at least one of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)) is preferred from the viewpoint of improving lithium ion conductivity.

[0017] When the solid electrolyte of the present invention has a crystalline phase of an argyrodite-type crystal structure, the above-mentioned diffraction peak A corresponds to the 110 plane in the crystal structure. Diffraction peak B corresponds to the 002 plane in the argyrodite-type crystal structure. Diffraction peak C corresponds to the 220 plane in the argyrodite-type crystal structure. Diffraction peak D corresponds to the 311 plane in the argyrodite-type crystal structure.

[0018] The solid electrolyte of the present invention preferably exhibits a diffraction peak different from the X-ray diffraction peaks known in conventional solid electrolytes containing a crystalline phase having an argyrodite-type crystal structure. Specifically, the solid electrolyte of the present invention preferably has a diffraction peak E at 2θ = 22.0° ± 0.5° and a diffraction peak F at 2θ = 22.9° ± 0.5°. The ranges of these diffraction peaks are each independently preferably ±1.0°, more preferably ±0.5°, and particularly preferably ±0.3°. The solid electrolyte of the present invention exhibits this diffraction peak, which makes it less likely to react with the active material even when a solid battery containing the solid electrolyte is stored at high temperatures in a charged state or when the solid battery is used in an unintentionally harsh environment, such as at high temperatures. This advantageously prevents a decrease in the recovery capacity of the solid battery and prevents an increase in the resistance of the solid battery. While the details of the substance exhibiting this diffraction peak are currently unclear, the present inventors have identified lithium phosphate (Li ) described below. ３ P.O. ４ ) I think this is the case.

[0019] The diffraction peak E is due to the main component of the solid electrolyte of the present invention, and the diffraction peak F is due to lithium phosphate (Li ３ P.O. ４ The present inventors believe that this is due to the fact that lithium phosphate has the effect of suppressing the increase in resistance at the interface between the solid electrolyte and the active material. Based on this, from the viewpoint of suppressing the increase in resistance at the interface between the solid electrolyte and the active material, the integrated intensity of the diffraction peak D is set to I Ｄ and the integrated intensity of the diffraction peak E is I Ｅ When I Ｅ / I Ｄ The value of is preferably 0.001 or more, more preferably 0.01 or more, and even more preferably 0.02 or more. In addition, since the ionic conductivity of lithium phosphate is considered to be lower than that of the main component in the solid electrolyte of the present invention, from the viewpoint of maintaining a high ionic conductivity of the solid electrolyte, Ｅ / IＤ The value of is preferably 0.5 or less, more preferably 0.1 or less, and even more preferably 0.05 or less.

[0020] I Ｅ / I Ｄ For the same reason as for setting the value of in the above range, in the solid electrolyte of the present invention, the integrated intensity of the diffraction peak D is set to I Ｄ and the integrated intensity of the diffraction peak F is I Ｆ When the above condition is satisfied, from the viewpoint of suppressing an increase in resistance at the interface between the solid electrolyte and the active material, I Ｆ / I Ｄ The value of I is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.3 or more. Ｆ / I Ｄ The value is preferably 5 or less, more preferably 2 or less, and even more preferably 1 or less.

[0021] As a result of investigations by the present inventors, it has been found that in order for the solid electrolyte of the present invention to exhibit the above-mentioned diffraction peaks A and B, it is advantageous to adjust the molar ratio of the X element to the P element (hereinafter also referred to as "X / P") to a relatively low value. In particular, when the molar ratio X / P is smaller than 1.2, the solid electrolyte of the present invention is likely to exhibit the diffraction peaks A and B. Furthermore, when the molar ratio X / P is smaller than 1.2, the above-mentioned intensity ratio I Ａ / I Ｂ From this viewpoint, the molar ratio X / P is preferably 1.0 or less, and more preferably 0.9 or less. The molar ratio X / P may be 0.1 or more, 0.4 or more, or 0.7 or more.

[0022] The molar ratio X / P being in the above range is advantageous in that the solid electrolyte of the present invention exhibits the above-mentioned diffraction peaks C and D. In addition, the molar ratio X / P being in the above range is advantageous in that the above-mentioned intensity ratio I Ｃ / I Ｄ It is also advantageous in that it makes it easier to achieve the above.

[0023] As a result of investigations by the present inventors, it has been found that adjusting the molar ratio of S element to P element (hereinafter also referred to as "S / P") is also advantageous in order for the solid electrolyte of the present invention to exhibit the above-mentioned diffraction peaks A and B. Specifically, when the molar ratio S / P is set to 4.6 or more, the solid electrolyte of the present invention is likely to exhibit the diffraction peaks A and B. Furthermore, when the molar ratio S / P is set to 4.6 or more, the above-mentioned intensity ratio I Ａ / I Ｂ From this viewpoint, the molar ratio S / P is preferably 4.7 or more, and more preferably 4.9 or more. The molar ratio S / P may be 6.0 or less, 5.5 or less, or 5.3 or less.

[0024] The molar ratio S / P being in the above range is advantageous from the viewpoint that the solid electrolyte of the present invention exhibits the above-mentioned diffraction peaks C and D. In addition, the molar ratio S / P being in the above range is advantageous from the viewpoint that the above-mentioned intensity ratio I Ｃ / I Ｄ It is also advantageous in that it makes it easier to achieve the above.

[0025] As described above, the solid electrolyte of the present invention preferably contains an oxygen element. Without being bound by theory, the present inventors speculate that either (i) the oxygen element is substituted for the sulfur (S) element in the argyrodite-type crystal structure, (ii) the oxygen element is contained in a substance other than the substance having the argyrodite-type crystal structure, or both (i) and (ii) are present. In the case of (i), the mixed anion effect resulting from the substitution of the sulfur (S) element with the oxygen (O) element is believed to maintain satisfactory lithium ion conductivity in the solid electrolyte, and when the solid electrolyte is used in a solid-state battery, the battery exhibits excellent battery characteristics. Specifically, the present inventors believe that the substitution of the sulfur (S) element in the argyrodite-type crystal structure with the oxygen (O) element suppresses the exchange reaction between the oxygen (O) element contained in the positive electrode active material and the sulfur (S) element in the argyrodite-type crystal structure. In the case of (ii), it is believed that the solid-state battery using the solid electrolyte of the present invention exhibits excellent battery characteristics due to a substance other than the substance having an argyrodite-type crystal structure. While the identity of this substance remains a matter of speculation, the inventors believe that, considering the preferred method for producing the solid electrolyte described below, this substance is likely the lithium phosphate described above. One of the challenges of solid-state batteries is that when a non-sulfide positive electrode active material contacts and reacts with a sulfide solid electrolyte, a high-resistance decomposition product is generated at the interface, increasing the interfacial resistance of the battery. One such high-resistance product is lithium phosphate. Therefore, the inventors believe that by pre-existing the decomposition product lithium phosphate at the interface between the positive electrode active material and the sulfide solid electrolyte, the generation of lithium phosphate resulting from the reaction between the positive electrode active material and the sulfide solid electrolyte can be suppressed. Furthermore, the inventors believe that the generation of lithium phosphate is also suppressed at the three-phase interface between the sulfide solid electrolyte, the positive electrode active material, and lithium phosphate, thereby suppressing the increase in interfacial resistance. Furthermore, because lithium phosphate has ionic conductivity, it is unlikely to inhibit ionic conduction between the positive electrode active material and the sulfide solid electrolyte, and it is expected that good battery characteristics can be obtained.

[0026] As a result of the inventor's investigations, it has been found that it is advantageous to adjust the molar ratio of O to P (hereinafter also referred to as "O / P") to a relatively low value. Specifically, when the molar ratio O / P is less than 1.0, a solid battery having the solid electrolyte of the present invention exhibits excellent battery characteristics, for example, even when the solid battery is stored in a charged state under a high-temperature environment, it is possible to suppress a decrease in the recovery capacity of the solid battery and to suppress an increase in the resistance of the solid battery. To further enhance this advantage, the molar ratio O / P is preferably 0.7 or less, and more preferably 0.3 or less. The molar ratio O / P may be greater than 0.001, or may be 0.05 or more, or may be 0.1 or more.

[0027] In the solid electrolyte of the present invention, the molar ratio of Li to P (hereinafter also referred to as "Li / P") is preferably, for example, 3.0 or more, more preferably 4.0 or more, and particularly preferably 5.0 or more. On the other hand, the molar ratio Li / P is preferably, for example, 7.0 or less, more preferably 6.9 or less, and particularly preferably 6.5 or less. When the molar ratio Li / P is within this range, the argyrodite-type crystal structure, particularly the cubic argyrodite-type crystal structure, becomes more stable at around room temperature (25°C), allowing lithium ion vacancies to be sufficiently introduced into the structure, resulting in effectively increasing lithium ion conductivity.

[0028] The solid electrolyte of the present invention preferably has a small particle size and high crystallinity. High crystallinity means that the solid electrolyte has few reactive sites. Therefore, even when a solid battery containing the solid electrolyte of the present invention is stored at high temperatures in a charged state or when the solid battery is used in an unintentionally harsh environment, such as at high temperatures, it is less likely to react with the active material, thereby achieving advantageous effects such as suppressing a decrease in the recovered capacity of the solid battery and suppressing an increase in the resistance of the solid battery. The crystallinity of the solid electrolyte can be evaluated by the half-width of the X-ray diffraction peak. The smaller the half-width value, the higher the crystallinity of the solid electrolyte can be evaluated. In the solid electrolyte of the present invention, the half-width of diffraction peak D is preferably 0.3° or less, more preferably 0.2° or less, and even more preferably 0.14° or less. The reason for selecting diffraction peak D for evaluating the half-width is that diffraction peak D is the peak with the greatest intensity in the solid electrolyte of the present invention, making it easy to calculate the half-width.

[0029] The solid electrolyte of the present invention has a volume cumulative particle size D at 50% cumulative volume by a laser diffraction / scattering particle size distribution measurement method. ５０ The particle size D is preferably less than 2.0 μm, more preferably 1.5 μm or less, and even more preferably 1.2 μm or less. By having such a particle size, the contact points and contact area between the solid electrolyte and the active material particles become large, and the input / output characteristics of the battery can be effectively improved. ５０ There is no particular limitation on the lower limit of the particle size, and it may be, for example, 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more. By having such a particle size, an excessive increase in the surface area of ​​the solid electrolyte can be suppressed, and an increase in resistance can be suppressed. In addition, it becomes easy to mix with the active material.

[0030] The solid electrolyte of the present invention has lithium ion conductivity in a solid state. The solid electrolyte preferably has a lithium ion conductivity of 0.5 mS / cm or more at room temperature, i.e., 25°C, more preferably 1.5 mS / cm or more, and particularly preferably 2.5 mS / cm or more. The lithium ion conductivity can be measured using the method described in the Examples below.

[0031] [Method for Producing Solid Electrolyte] Next, a preferred method for producing the solid electrolyte of the present invention will be described. The solid electrolyte can be preferably produced by a solid-phase reaction in which a raw material composition is heated and sintered. The raw material composition is a mixture of raw material powders containing the above-mentioned elements that constitute the solid electrolyte. The raw material composition contains one or more compounds containing at least one of Li, P, S, O, and X.

[0032] The raw material powder may be, for example, a compound containing an Li element, a compound containing an S element, a compound containing a P element, a compound containing an O element, or a compound containing an X element.

[0033] The raw material powder may contain at least two or more elements selected from Li, P, S, O, and X in one compound. For example, the raw material powder may be a compound containing Li and X, a compound containing P and S, a compound containing Li and S, a compound containing P and X, a compound containing S and X, a compound containing Li and O, or a compound containing P and O. An example of the compound containing Li and X is lithium halide. An example of the compound containing P and S is diphosphorus trisulfide (P ２ S ３ ) and diphosphorus pentasulfide (P ２ S ５ As a compound containing Li and S, for example, lithium sulfide (Li ２ As a compound containing P element and X element, for example, PX３ and P ２ X ５ Examples of compounds containing S and X elements include SX ２ , SX ４ , SX ６ , S ２ X １０ Examples of compounds containing Li and O include lithium oxide (Li ２ O), lithium carbonate (Li ２ CO ３ ), sodium phosphate (Na ３ P.O. ４ ), and POCl ３ Examples of compounds containing P and O include diphosphorus pentoxide (P ２ O ５ ) etc.

[0034] The raw material powders are preferably subjected to a pulverization process to adjust the particle size to a predetermined size before mixing. Pulverization can be performed using a media-agitated mill, such as a ball mill or a bead mill. When pulverization is performed using a media-agitated mill, a slurry of the raw material powder is placed in a container, ceramic or metal balls or beads are placed in the container, and the container is rotated to cause the raw material powder to collide with the balls or beads within the container, thereby pulverizing the raw material powder. Although pulverization tends to reduce the crystallinity of the raw material powder, in this production method, pulverization is preferably performed so as to minimize the reduction in the crystallinity of the raw material powder to be pulverized. This pulverization process can produce a solid electrolyte with a small particle size and high crystallinity, thereby satisfying the above-mentioned X-ray intensity ratio. From this perspective, it is advantageous to use a resin container for pulverization using a media-agitated mill. Resin containers have the advantage of being less hard than metal or ceramic containers, making them less likely to reduce crystallinity during pulverization. As the resin container, for example, containers made of various thermoplastic resins such as polyamide, polyethylene, polypropylene, and polyethylene terephthalate can be used.

[0035] After the grinding of the raw material powders is completed, the raw material powders are mixed to obtain a raw material composition. The raw material powders are preferably mixed so that the molar ratio X / P in the target solid electrolyte is, for example, smaller than 1.2, since this facilitates the production of a solid electrolyte that satisfies the above-mentioned strength ratio. From the same viewpoint, the raw material powders are preferably mixed so that the molar ratio O / P in the target solid electrolyte is, for example, larger than 0.001 and smaller than 1.0.

[0036] It is also preferable to use a media-agitating mill for mixing the raw material powders. In this case, it is preferable to mix the raw material powders in a manner that minimizes the decrease in crystallinity. By performing such mixing, a solid electrolyte having a small particle size and high crystallinity can be obtained, and as a result, a solid electrolyte that satisfies the above-mentioned strength ratio can be obtained. From this perspective, it is advantageous to use a resin container for mixing using a media-agitating mill. As the resin container, the same resin container as that used for pulverizing the raw material powders can be used without any particular restrictions.

[0037] Next, the raw material composition is subjected to a calcination process to cause a solid-state reaction and obtain a crystalline calcined product. The calcination atmosphere can be, for example, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere, or a hydrogen sulfide atmosphere. From the viewpoint of adjusting the ratio of sulfur element contained in the solid electrolyte, it is preferable to use an inert gas atmosphere.

[0038] From the viewpoint of ensuring that a solid-phase reaction of the raw material composition occurs, the firing temperature is, for example, preferably 200° C. or higher, more preferably 300° C. or higher, even more preferably 350° C. or higher, and even more preferably 400° C. or higher. On the other hand, in consideration of industrial producibility and economic efficiency, the firing temperature is, for example, preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 550° C. or lower.

[0039] The firing time is not critical, and may be any time that allows a fired product of the desired composition to be obtained. Specifically, the firing time is preferably long enough for the solid-phase reaction of the raw material composition to occur sufficiently. The firing time may be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time may be, for example, 10 hours or less, or 5 hours or less.

[0040] After firing, the fired product may be crushed or pulverized as needed, and further classified as needed. This allows the desired solid electrolyte powder to be obtained. For crushing or pulverization, it is preferable to use a media-agitating mill using a resin container. As mentioned above, this is to minimize the deterioration of the crystallinity of the fired product during crushing or pulverization.

[0041] [Electrode mixture and solid-state battery] The solid electrolyte thus obtained can be used alone or in combination with other solid electrolytes. For example, the solid electrolyte of the present invention can be used as a material for constituting a lithium battery, such as a solid electrolyte layer, a positive electrode layer, or a negative electrode layer.

[0042] Specifically, the solid electrolyte of the present invention can be used in a battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. In other words, the solid electrolyte can be used in so-called solid-state batteries. More specifically, it can be used in lithium solid-state batteries. The lithium solid-state battery may be a primary battery or a secondary battery. There is no particular limitation on the shape of the battery, and shapes such as a laminated type, a cylindrical type, and a prismatic type can be adopted. The term "solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substance as an electrolyte, but also batteries that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0043] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be produced, for example, by dropping a slurry consisting of the solid electrolyte, a binder, and a solvent onto a substrate and scraping it off with a doctor blade or the like, by contacting the substrate with the slurry and then cutting it with an air knife, or by forming a coating film by screen printing or the like and then heating and drying to remove the solvent. Alternatively, the solid electrolyte can be produced by compacting a powdered solid electrolyte by pressing or the like and then appropriately processing it. The thickness of the solid electrolyte layer is typically preferably 5 μm to 300 μm, and more preferably 10 μm to 100 μm, in order to balance short-circuit prevention and volumetric capacity density.

[0044] The solid electrolyte of the present invention can also be used together with an active material to form an electrode mixture. The proportion of the solid electrolyte in the electrode mixture is typically 10% by mass or more and 50% by mass or less. The electrode mixture may contain other materials such as a conductive material as needed. An electrode mixture, a binder, and a solvent are mixed to form a paste, which is then applied to a current collector such as aluminum foil and dried to form an electrode layer such as a positive electrode layer or a negative electrode layer.

[0045] The cathode material constituting the cathode layer can be any cathode material used as a cathode active material in lithium-ion batteries. For example, lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium transition metal oxides with layered structures, can be used. The use of a high-voltage cathode material as the cathode material can improve energy density. In addition to the cathode active material, the cathode material may contain a conductive material or other materials.

[0046] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as a negative electrode active material in a lithium ion battery can be appropriately used. Since the solid electrolyte of the present invention is electrochemically stable, it can be used at a potential of lithium metal or a lower potential comparable to that of lithium metal (about 0.1 V vs. Li ＋Carbonaceous materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), which are materials that are charged and discharged using a lithium-ion battery (Li / Li), can be used as the negative electrode material. This can significantly improve the energy density of solid-state batteries. Silicon or tin, which are promising high-capacity materials, can also be used as the active material. The negative electrode material may also contain a conductive material or other materials in addition to the negative electrode active material.

[0047] [Active Material] The present invention also provides an active material having a coating layer containing the above-described solid electrolyte on its surface. This active material will be described below. The active material of the present invention has a core particle and a coating layer disposed on the surface of the core particle. The core particle is a portion that occupies the majority of the active material and is composed of an active material base material. The coating layer is disposed on the surface of the core particle and forms the outermost surface of the active material.

[0048] The active material of the present invention is generally in the form of particles. The particle size of the active material is, for example, the volume cumulative particle size D at 50% cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ The particle diameter D of the active material is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. ５０ is preferably 20.0 μm or less, more preferably 15.0 μm or less, and even more preferably 10.0 μm or less. ５０ By setting the value of the resistance of the active material to within the above range, the resistance when lithium ions diffuse into the particles of the active material can be reduced, and as a result, the charge / discharge characteristics can be improved.

[0049] The active material of the present invention can be mixed with a solid electrolyte and a conductive material to obtain an electrode mixture. In this case, the same solid electrolyte as the solid electrolyte of the present invention described above can be used as the solid electrolyte. Alternatively, a solid electrolyte other than the solid electrolyte of the present invention can be used. When using a different solid electrolyte, it is preferable to use a solid electrolyte having a molar ratio X / P of, for example, 1.2 or more, particularly 1.4 or more, and particularly 1.5 or more. This can reduce reaction resistance and improve storage characteristics when the solid battery is exposed to high temperatures.

[0050] [Coating Layer of Active Material] The coating layer is composed of the above-described solid electrolyte. The solid electrolyte contained in the coating layer preferably contains a crystalline phase having an argyrodite-type crystal structure. The solid electrolyte contained in the coating layer preferably contains Li, P, S, O, and X, and the molar ratio of O to P is preferably greater than 0.001 and less than 1.0. The solid electrolyte contained in the coating layer preferably has a molar ratio X / P of X to P less than 1.2. A solid battery including an active material having a coating layer containing such a solid electrolyte can suppress a decrease in the recovery capacity of the solid battery and an increase in the resistance of the solid battery, even when stored in a charged state under high-temperature conditions, due to the action of the coating layer. From this perspective, the ratio of the coating layer to the active material of the present invention is preferably, for example, 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. The ratio of the coating layer to the active material of the present invention is preferably, for example, 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. The method for measuring the ratio of the coating layer to the active material is as follows.

[0051] [Method for Measuring the Ratio of Coating Layer to Active Material] A PHI Quantes XPS device manufactured by ULVAC-PHI, Inc. is used. Specifically, the ratio of the quantitative value of elements present only in the coating portion to the sum of the quantitative value of elements present only in the coating portion and the quantitative value of elements present only in the core material particles is calculated. For example, when LNMO (a spinel-type lithium transition metal composite oxide having a composition of Li: 4.1 mass%, Mn: 41.3 mass%, Ni: 13.3 mass%, Ti: 5.4 mass%) is used as the core material particles and a sulfide solid electrolyte containing Li, P, S, and X elements is used as the coating portion, the coating ratio is calculated by (S + P + X) / (Mn + Ni + Ti + S + P + X) × 100. Similarly, for example, when NCM (LiNi ０．５ Co ０．２ Mn ０．３ O ２ When a sulfide solid electrolyte containing Li, P, S, and X elements is used as the coating portion, the coverage is calculated by (S + P + X) / (Ni + Co + Mn + S + P + X) × 100. The conditions used for the measurement are as follows: Excitation X-ray: Monochromated Al beam (1486.7 eV) Output: 50 W Acceleration voltage: 15 kV X-ray irradiation diameter: 200 μmφ Measurement area: 1000 μm × 300 μm Take of angle: 45° Pass energy: 26.0 eV Energy step: 0.1 eV

[0052] The thickness of the coating layer is preferably within a predetermined range. Specifically, the thickness of the coating layer is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. The thickness of the coating layer is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less. By setting the thickness of the coating layer within the above range, an excessive increase in the interface resistance caused by the formation of the coating layer is suppressed, and the coating layer can function as a good lithium ion conductive layer.

[0053] The thickness of the coating layer can be measured by, for example, X-ray photoelectron spectroscopy (XPS). If necessary, it can also be measured by observation using a scanning transmission electron microscope (STEM) in combination with Auger electron spectroscopy (AES).

[0054] The coating layer may be absent from some portions of the surface of the core particle. In this case, the coating layer is preferably disposed on 30% or more of the entire surface area of ​​the core particle, more preferably 50% or more, and even more preferably 80% or more (this value is also referred to as the "coverage rate"). From the viewpoint of suppressing the reaction between the active material and the solid electrolyte and improving the storage characteristics of the battery, the higher the coverage rate, the more preferable. The coating layer may be disposed on 100% or less of the entire surface area of ​​the core particle. The coverage rate can be confirmed, for example, by observing the surface of the core particle using X-ray photoelectron spectroscopy (XPS) in combination with, if necessary, a scanning transmission electron microscope (STEM) and energy dispersive X-ray analysis (EDS), as described above, in addition to Auger electron spectroscopy (AES). The thickness of the coating layer disposed on the surface of the core particle does not need to be uniform.

[0055] In the active material of the present invention, as long as a coating layer containing the above-mentioned solid electrolyte is disposed on the outermost surface of the active material, one or more intermediate layers may be disposed between the core particle and the coating layer. The intermediate layer is preferably composed of at least one selected from the group consisting of lithium sulfate, lithium phosphate, lithium sulfide, and lithium halide. Alternatively, the intermediate layer may be, for example, LiNbO ３ , LiNbO and Li ３ NbO ４ It is preferable that the intermediate layer contains a compound such as a lithium niobium composite oxide, lithium tantalate, or lithium zirconate. These compounds can be used alone or in combination of two or more. When the intermediate layer contains these compounds, the preferred proportion of the compound is 0.1% by mass or more and 5.0% by mass or less relative to the core particles.

[0056] Examples of the lithium salt of phosphoric acid contained in the intermediate layer include lithium orthophosphate, lithium pyrophosphate, lithium metaphosphate, and lithium polyphosphate. Among these, from the viewpoint of more effectively suppressing the oxidation reaction of the solid electrolyte, it is preferable to use lithium pyrophosphate as the lithium salt of phosphoric acid, and it is more preferable to use lithium metaphosphate.

[0057] In the active material of the present invention, when an intermediate layer is disposed between the core particle and the coating layer, it is preferable that the oxygen content in the coating layer be lower than that in the intermediate layer. In other words, it is preferable that there is a gradient in the oxygen content between the intermediate layer and the coating layer. By providing such a gradient, the S—O exchange reaction between the active material and the solid electrolyte is less likely to occur, thereby suppressing a deterioration in the battery characteristics of the solid-state battery.

[0058] [Core Particle] The core particle is not particularly limited as long as it functions as an active material. The core particle may contain, for example, a lithium metal composite oxide. As the lithium metal composite oxide, a known lithium metal composite oxide can be used. For example, the core particle may be a lithium metal composite oxide represented by the general formula LiM ２ O ４ (M represents a metal element), a lithium transition metal composite oxide having a spinel structure represented by the general formula LiMO ２ (M represents a metal element), a lithium transition metal composite oxide having a layered rock salt structure represented by the general formula LiMPO ４ (M represents a metal element). Alternatively, it may be a combination of two or more of these. However, it is not limited to these.

[0059] [Core Particle A] The core particle is preferably a particle made of a lithium transition metal composite oxide having a spinel structure, containing Li, Mn, and O and one or more other elements (hereinafter, this core particle will also be referred to as "core particle A"). When the active material of the present invention containing core particle A is used as a positive electrode active material, it has an operating potential of 4.5 V or higher relative to metallic Li. "Having an operating potential of 4.5 V or higher relative to metallic Li" does not necessarily mean that the plateau region only has an operating potential of 4.5 V or higher, but also includes cases where the plateau region also has an operating potential of 4.5 V or higher. Therefore, the present invention is not limited to a positive electrode active material consisting solely of a 5V-class positive electrode active material having an operating potential of 4.5 V or higher in the plateau region. For example, the active material of the present invention may also contain a positive electrode active material having an operating potential of less than 4.5 V in the plateau region. Specifically, it is preferable that the 5V-class positive electrode active material occupies, for example, 30% by mass or more, preferably 50% by mass or more, and particularly preferably 80% by mass or more (including 100% by mass) of the positive electrode active material.

[0060] As described above, the core particle A is preferably a particle made of a spinel-type composite oxide containing Li, Mn, and O and two or more other elements. At least one of the "two or more other elements" is preferably a metal element M1 selected from the group consisting of Ni, Co, and Fe, and the other element is preferably a metal element M2 consisting of one or a combination of two or more selected from the group consisting of Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce.

[0061] A preferred composition example of the core particle A is LiMn ２ O ４－δ Examples of the lithium-manganese-containing spinel composite oxide include those having a crystal structure in which a part of the Mn sites in the formula (I) is substituted with Li, a metal element M1, and another metal element M2.

[0062] The metal element M1 is a substitution element that mainly contributes to realizing an operating potential of 4.5 V or more relative to the metallic Li reference potential, and examples thereof include Ni, Co, and Fe. The active material A may contain at least one of these elements, and it is particularly preferable that the active material A contains at least one element selected from Ni and Co.

[0063] The metal element M2 is a substitution element that mainly contributes to stabilizing the crystal structure and improving characteristics. Examples of substitution elements that contribute to improving the capacity retention rate include Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Among these, Na, Mg, Al, K, Ca, Ti, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, Ta, and W are preferred. The metal element M2 may be one or a combination of two or more of the above-mentioned elements. The metal element M2 preferably contains at least one of the above-mentioned elements, and may also contain a metal element other than the above-mentioned elements. The metal element M2 contained in the structure is a different element species from the metal element M1.

[0064] An example of the composition of the core particle A is a compound represented by the formula (1): Li １＋ｘ (M1 ｙ M2 ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ The metal element M1 and the metal element M2 in the formula (1) are as described above.

[0065] In the formula (1), "x" is preferably 0.001 or more. In the formula (1), "x" is preferably 0.2 or less. "y," which indicates the content of the metal element M1, is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. "y," which indicates the content of the metal element M1, is preferably 1.20 or less, more preferably 1.10 or less, and even more preferably 1.05 or less. "z," which indicates the content of the metal element M2, is preferably 0.001 or more, more preferably 0.002 or more, more preferably 0.005 or more, and even more preferably 0.100 or more. Setting "z" to 0.100 or more can more effectively improve cycle characteristics. "z," which indicates the content of the metal element M2, is preferably 0.400 or less, and even more preferably 0.300 or less.

[0066] Another example of the composition of the core particle A is a compound represented by the formula (2): Li １＋ｘ (Ni ｙ M3 ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ Examples of the spinel-type lithium manganese-containing composite oxide include those represented by the formula (2). In formula (2), "x" is preferably 0.001 or more, for example. In formula (2), "x" is preferably 0.2 or less, for example. In formula (2), "y" is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. In formula (2), "y" is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.

[0067] In the formula (2), examples of the metal element M3 include Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Of these, Na, Mg, Al, K, Ca, Ti, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, Ta, and W are preferred. The metal element M3 may be one or a combination of two or more of the aforementioned elements. "z," which indicates the molar ratio of the metal element M3, is preferably 0 or greater, more preferably greater than 0.01, even more preferably 0.05 or greater, and even more preferably 0.10 or greater. By setting "z" to the lower limit or greater, the cycle characteristics can be more effectively improved. Furthermore, "z" indicating the molar ratio of the metal element M3 is preferably, for example, 0.50 or less, more preferably 0.45 or less, even more preferably 0.40 or less, and even more preferably 0.35 or less.

[0068] In addition, "4-δ" in the above formulas (1) and (2) indicates that oxygen vacancies may be present. Furthermore, a portion of the oxygen may be substituted with fluorine or other elements. In this case, δ is preferably 0 or more. Furthermore, δ is preferably, for example, 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less.

[0069] The core particle A may contain components other than the above-mentioned Li, Mn, metal element M1, metal element M2, metal element M3, O, and B. In particular, the other elements may be contained in an amount of 0.5 mass% or less, because such amounts are considered to have little effect on the performance of the core particle.

[0070] Note that, when core particle A is fitted to a cubic crystal structure model of space group Fd-3m (Origin Choice 2), for example, the ranges of Rwp and S, which indicate the degree of agreement between observed intensity and calculated intensity, are Rwp<10 or S<2.5, and thus it can be confirmed that core particle A has a spinel structure.

[0071] The primary particles of the core particles A are preferably polycrystalline rather than single crystalline. A single crystal refers to a particle in which the primary particle is composed of one crystallite, and a polycrystalline refers to a particle in which multiple crystallites exist within the primary particle. Whether the core particles are polycrystalline or not can be confirmed by observing the cross section of the primary particle using electron backscatter diffraction (EBSD). In the case of a polycrystalline particle, it can be confirmed that crystals with multiple orientations exist within the primary particle.

[0072] [Core Particle B] The core particle is also preferably a particle made of a lithium transition metal composite oxide having a layered rock salt structure, containing Li, an M element (M includes at least one or a combination of two or more elements selected from the group consisting of Ni, Co, Mn, and Al), and O (hereinafter, this core particle will also be referred to as "core particle B"). The active material of the present invention may contain other components in addition to core particle B. However, from the viewpoint of effectively obtaining the properties of core particle B, it is preferable that core particle B accounts for, for example, 80% by mass or more, preferably 90% by mass or more, and of these, 95% by mass or more (including 100% by mass).

[0073] The core particle B is represented by the formula (3): Li １＋ｘ M １－ｘ O ２ (wherein M is a combination of one or more elements selected from the group consisting of Ni, Co, Mn, and Al, or includes a combination of one or more elements selected from the group consisting of Ni, Co, Mn, and Al and a combination of one or more elements selected from the group consisting of transition metal elements present in Groups 3 to 11 of the periodic table and typical metal elements from Periods 1 to 3 of the periodic table).

[0074] Formula (3): Li １＋ｘ M １－ｘ O ２ In the formula (3), "1+x" is, for example, 0.95 or more, preferably 0.97 or more, and more preferably 0.98 or more. １＋ｘ M １－ｘO ２ In the above formula, "1+x" is preferably, for example, 1.09 or less, more preferably 1.07 or less, and even more preferably 1.05 or less.

[0075] "M" in the formula (3) may contain the three elements Mn, Co, and Ni. For example, it may be composed of only the three elements Mn, Co, and Ni, or may contain one or more of the other elements in addition to the three elements, or may have another configuration.

[0076] Examples of the transition metal elements present among the elements of Groups 3 to 11 of the periodic table and the typical metal elements of the first to third periods of the periodic table include Al, V, Fe, Ti, Mg, Cr, Ga, In, Cu, Zn, Nb, Zr, Mo, W, Ta, and Re, and among these, V, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb, Zr, Mo, W, and Ta are preferred.

[0077] When "M" in the formula (3) contains the three elements Mn, Co, and Ni, the molar ratios of Mn, Co, and Ni are preferably Mn:Co:Ni = greater than 0.00 and not greater than 0.45: greater than 0.00 and not greater than 0.40: 0.30 or more and not greater than 1.00, and more preferably Mn:Co:Ni = 0.01 or more and not greater than 0.45: 0.01 or more and not greater than 0.40: 0.30 or more and not greater than 0.95, and among these, Mn:Co:Ni = 0.05 or more and not greater than 0.40: 0.03 or more and not greater than 0.40: 0.30 or more and not greater than 0.85, and among these, Mn:Co:Ni = 0.05 or more and not greater than 0.40: 0.03 or more and not greater than 0.40: 0.30 or more and not greater than 0.75 is even more preferable.

[0078] In the above formula (3), the atomic ratio of the oxygen amount is written as "2" for convenience, but may have some degree of non-stoichiometry. That is, the atomic ratio of the oxygen amount may be "2-δ", where "-δ" indicates oxygen deficiency. In this case, δ is preferably 0 or more. Furthermore, δ is preferably, for example, 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less.

[0079] The core particles B may contain impurities. For example, the core particles B may contain 0.17% by mass or less of each impurity element. This is because such amounts are thought to have little effect on the properties of the core particles B.

[0080] When the core particle B is fitted to a hexagonal crystal structure model of space group R-3m, for example, the ranges of Rwp and S, which indicate the degree of agreement between the observed intensity and the calculated intensity, are Rwp<10 or S<2.5, whereby it can be confirmed that the core particle B has a layered structure.

[0081] The primary particles of core particle B are preferably polycrystalline rather than single crystalline, similar to core particle A. The definitions of single crystal and polycrystalline are the same as those for core particle A.

[0082] [Core Particle C] The core particle is preferably a particle made of a lithium-excess layered rock-salt type lithium-containing composite oxide containing Li, Ma (Ma necessarily contains Mn and also contains at least one selected from Ni and Co), Mb (Mb contains at least one selected from Al, Mg, Ti, Fe, and Nb), and O (hereinafter, this core particle will also be referred to as "core particle C"). The active material of the present invention may contain other components in addition to the core particle C. However, from the viewpoint of effectively obtaining the properties of the core particle C, it is preferable that the core particle C accounts for, for example, 50% by mass or more, particularly 70% by mass or more, of which 90% by mass or more, and of which 95% by mass or more (including 100% by mass) is preferred.

[0083] The core particle C is represented by the formula (5): Li １＋ｘ Ma １－ｘ－ｙ Mb ｙ O ２ (wherein Ma necessarily contains Mn and also contains at least one selected from Ni and Co; and Mb contains at least one selected from Al, Mg, Ti, Fe, and Nb).

[0084] In the formula (5), "x" is, for example, preferably 0.10 or more, more preferably 0.11 or more, and even more preferably 0.12 or more. In the formula (5), "x" is, for example, preferably 0.33 or less, more preferably 0.32 or less, and even more preferably 0.31 or less. In the formula (5), "y" is, for example, preferably 0.000 or more, more preferably 0.005 or more, and even more preferably 0.010 or more. In the formula (5), "y" is, for example, preferably 0.300 or less, more preferably 0.295 or less, and even more preferably 0.290 or less.

[0085] Regarding the content of Ma in the core particle, the content of Mn in Ma is, for example, preferably 30% by mass or more, more preferably 31% by mass or more, and even more preferably 32% by mass or more, and the content of Mn in Ma is, for example, preferably 80% by mass or less, more preferably 79% by mass or less, and even more preferably 78% by mass or less.

[0086] In the above formula (5), the atomic ratio of the oxygen amount is written as "2" for convenience, but may have some degree of non-stoichiometry. That is, the atomic ratio of the oxygen amount may be "2-δ", where "-δ" indicates oxygen deficiency. In this case, δ is preferably 0 or more. Furthermore, δ is preferably, for example, 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less.

[0087] The core particles C may contain impurities. For example, SO 4 may be used as the impurity. ４ When SO is contained, it may contain 1.0 mass % or less as an impurity. ４ When elements other than those mentioned above are contained, they may be contained in an amount of 0.5 mass % or less, because it is believed that such an amount will have almost no effect on the properties of the core particles C.

[0088] [Method for Producing Active Material] Methods for producing active materials are broadly divided into methods for producing core particles and methods for forming a coating layer on the surface of core particles. An example of a method for producing core particles is a production method comprising a raw material mixing step, a wet-pulverization step, a granulation step, a firing step, and a pulverization step. However, this production method is a preferred example, and the present invention is not limited to this production method.

[0089] The method for forming a coating layer includes the steps of preparing a coating powder and disposing a coating layer containing the coating powder on the surface of a core particle. In the step of preparing the coating powder, the solid electrolyte of the present invention is prepared. The solid electrolyte has a particle diameter D ５０ The particle size D of the solid electrolyte is preferably adjusted to 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. ５０ is preferably adjusted to 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.9 μm or less. By doing so, the coating layer can be successfully disposed on the surface of the core particle.

[0090] In the step of disposing a coating layer on the surface of the core particles, the coating powder and the core particles are dry-mixed. For example, a media agitation mill can be used for the dry mixing. The powder of the core particles has a particle diameter D ５０ The particle diameter D of the core particle powder is preferably adjusted to 1 μm or more, more preferably 2 μm or more, and even more preferably 2.5 μm or more. ５０ is preferably adjusted to 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. By doing so, the coating layer can be successfully disposed on the surface of the core particle.

[0091] By performing the dry mixing while cooling, the coating powder is less likely to deteriorate. As a result, the battery characteristics of a solid-state battery including the obtained active material are less likely to deteriorate, which is preferable. In this case, for example, a dry mixer equipped with a water-cooling jacket can be used. The temperature of the mixture during dry mixing is preferably maintained at 10°C or higher and 50°C or lower.

[0092] In relation to the above-described embodiments, the present invention further discloses the following solid electrolyte, active material, electrode mixture, electrode layer, and solid-state battery. <1> A solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X), wherein the molar ratio of the halogen (X) to the phosphorus (P) is less than 1.2, and the molar ratio of the oxygen (O) to the phosphorus (P) is greater than 0.001 and less than 1.0, and wherein an X-ray diffraction pattern measured with an X-ray diffractometer using CuKα radiation has diffraction peaks at 2θ = 15.4° ± 1° and 2θ = 17.8° ± 1°. <2> In the X-ray diffraction pattern, the integrated intensity of the diffraction peak observed at 2θ = 15.4° ± 1° is defined as I Ａ The integrated intensity of the diffraction peak observed at 2θ = 17.8° ± 1° is defined as I Ｂ When the integrated intensity of the diffraction peak observed at 2θ = 25.3° ± 1° is expressed as I Ｃ The integrated intensity of the diffraction peak observed at 2θ = 29.7° ± 1° is defined as I Ｄ When this is done, I Ａ / I Ｂ The value of is 0.70 or more, and I Ｃ / I Ｄ <3> The solid electrolyte according to <1>, wherein the value of the volume cumulative particle diameter D at 50% by volume cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method is 0.91 or less. ５０<2> The solid electrolyte according to <2>, wherein the X-ray diffraction pattern has a mean particle size of less than 2.0 μm, and the half-width of a diffraction peak observed at 2θ = 29.7° ± 1° is 0.3° or less. <4> The solid electrolyte according to any one of <1> to <3>, wherein the X-ray diffraction pattern has diffraction peaks at 2θ = 22.0° ± 0.5° and 2θ = 22.9° ± 0.5°. <5> An active material comprising: a core particle and a coating layer disposed on at least a part of a surface of the core particle, the coating layer containing a solid electrolyte including a crystalline phase having an argyrodite-type crystal structure, the solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and a halogen (X), and wherein the molar ratio of oxygen (O) to phosphorus (P) is greater than 0.001 and less than 1.0. <6> The active material according to <5>, wherein the core particle comprises at least one selected from a lithium transition metal composite oxide having a layered rock-salt structure, a lithium transition metal composite oxide having a spinel structure, and a phosphate compound having an olivine structure. <7> The active material according to <5> or <6>, wherein the solid electrolyte has a molar ratio of halogen (X) element to phosphorus (P) element of less than 1.2. <8> The active material according to any one of <5> to <7>, wherein the proportion of the coating layer relative to the active material is 0.1% by mass or more and 10% by mass or less. <9> An electrode mixture comprising the solid electrolyte according to any one of <1> to <4> or the active material according to any one of <5> to <8>, and a conductive material. <10> The electrode mixture according to <9>, wherein the active material according to any one of <5> to <8>, the conductive material, and a solid electrolyte, wherein the solid electrolyte has a molar ratio of halogen (X) element to phosphorus (P) element of 1.2 or more. <11> An electrode layer comprising the electrode mixture according to <9> and a binder. <12> A solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises the electrode mixture according to <9>.

[0093] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0094] [Example 1] (1) Production of solid electrolyte Lithium sulfide (Li ２ S) powder, lithium oxide (Li ２ O) powder, diphosphorus pentasulfide (P ２ S ５ Lithium chloride (LiCl) powder, lithium bromide (LiBr) powder, and lithium fluoride (LiBr) powder were used as raw material powders. Each raw material powder was weighed and mixed to obtain the composition shown in Table 1 below, and heptane was added to prepare a slurry. This slurry was placed in a polyamide container and set in a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as the grinding media. The ball mill was operated at 100 rpm, and wet mixing was performed for 10 hours. The mixed slurry was vacuum dried at room temperature to remove the heptane. In this way, a raw material composition was obtained.

[0095] The raw material composition was fired to obtain a fired product. The firing was carried out using a tubular electric furnace. Nitrogen gas with a purity of 100% was circulated through the electric furnace during firing. The firing temperature was increased to 500°C at a rate of 200°C / h and maintained at 500°C for 4 hours. In this manner, a fired product was obtained.

[0096] The obtained fired product was crushed in a mortar and passed through a 250 μm sieve to obtain a crushed powder. This crushed powder was crushed in a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as crushing media. The container was made of polyamide. Heptane was used as the solvent. The ball mill was operated at 100 rpm, and crushing was carried out for 3 hours. The obtained slurry was vacuum dried at room temperature to remove the solvent. In this way, the particle size D ５０ A powder of solid electrolyte having a particle size of 3 μm was obtained.

[0097] The obtained powder was pulverized using a planetary ball mill. Zirconia balls with a diameter of 0.8 mm were used as the pulverization media. The container was made of zirconia. Toluene was used as the solvent. The ball mill was operated at 100 rpm, and the pulverization was carried out for 1 hour. The obtained slurry was vacuum dried at room temperature to remove the solvent. In this way, the particle size D ５０ A solid electrolyte having a thickness of 1.0 μm was obtained.

[0098] (2) Production of active material As a core particle, a particle diameter D ５０ LiCo having a thickness of 2.6 μm ０．６ Ni ０．２ Mn ０．２ O ２ were prepared. The solid electrolyte and core particle powder were mixed using a dry particle compositing device NOB-MINI manufactured by Hosokawa Micron Corporation, and the solid electrolyte was attached to the surface of the core particles to form a coating layer containing the solid electrolyte. The amount of solid electrolyte relative to the total amount of core particles and solid electrolyte was adjusted to the value shown in Table 1. During mixing, the device was cooled and maintained at 30°C. In this way, active material particles were obtained.

[0099] Comparative Example 1: Li was added to obtain the composition shown in Table 1 below. ２ S powder and P ２ S ５ The powder, LiCl powder, and LiBr powder were weighed to obtain a raw material composition. A solid electrolyte and an active material were obtained in the same manner as in Example 1, except for the above.

[0100] [Evaluation] The solid electrolytes obtained in the examples and comparative examples were subjected to X-ray diffraction measurement by the following method, and the intensity ratio I Ａ / I Ｂ , I Ｃ / I Ｄ , I Ｅ / I Ｄ and I Ｆ / I Ｄ The value of the half-width of the diffraction peak D was also determined. ５０ The X-ray diffraction charts for the solid electrolytes of the Examples and Comparative Examples are shown in Figure 1. The conductivity of the solid electrolytes obtained in the Examples and Comparative Examples was also measured. Furthermore, solid batteries were manufactured using the active materials obtained in the Examples and Comparative Examples, and the reaction resistance increase rate and capacity recovery rate of the solid batteries after storage at 90°C were measured using the following methods. The results are shown in Table 1 below.

[0101] [X-ray diffraction measurement] Measurements were performed using a Malvern Panalytical tabletop X-ray diffractometer "Aeris" without exposure to air. The measurement conditions were as follows: - Radiation source: CuKα - Tube voltage: 40 kV - Tube current: 15 mA - Measurement method: Focusing method (reflection method) - Detector: One-dimensional semiconductor detector - Incident Soller slit: Soller slit 0.02 rad - Longitudinal limiting slit: 20 mm - Receiving Soller slit: 0.02 rad - Incident slit: 1 / 2° - Receiving slit: Open - Measurement range: 2θ = 10 to 105° - Step width: 0.01° - Scan speed: 1.67° / min. The background intensity obtained from the Kapton film in the non-exposed holder was subtracted before analyzing the measurement results.

[0102] [Integrated Intensity and Full Width at Half Maximum] The X-ray diffraction pattern obtained by X-ray diffraction measurement was loaded into Smart Lab Studio II and calculated by peak processing. Peak profiling was performed using a divided pseudo-Voight function for peak shape, a B-spline background type, and automatic fitting conditions. From the resulting peak list, the integrated intensity (Count °) and full width at half maximum FWHM (°) of the corresponding peak were read.

[0103] [Particle size D ５０ The solid electrolyte was added to toluene using an automatic sample feeder for a laser diffraction particle size distribution analyzer ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), and irradiated with 40 W ultrasonic waves for 360 seconds at a flow rate of 40%, and then the particle size distribution was measured using a laser diffraction particle size distribution analyzer "MT3000II" manufactured by Nikkiso Co., Ltd. The particle size D ５０ was measured.

[0104] [Conductivity] The solid electrolyte was measured in a glove box purged with sufficiently dried Ar gas (dew point -60°C or less) to obtain a conductivity of about 6 t / cm ２The pellets were subjected to uniaxial pressure molding under a load of 1000 kJ / cm2 and approximately 0.5 to 8 mm thick to prepare samples for measuring lithium ion conductivity. The lithium ion conductivity of the samples was measured using a Solartron 1255B impedance measuring device manufactured by Toyo Corporation. The measurements were performed by the AC impedance method at a temperature of 25°C and a frequency of 0.1 Hz to 1 MHz.

[0105] [Reaction Resistance and Capacity Recovery Rate] (1) [Fabrication of Solid-State Battery] The active materials obtained in the Examples and Comparative Examples were used as the positive electrode active material, and graphite powder was used as the negative electrode active material. ５．４ P.S. ４．４ Cl ０．８ Br ０．８ A sulfide solid electrolyte containing a crystalline phase having an argyrodite-type crystal structure was used. A positive electrode active material, a solid electrolyte, and a conductive carbon additive were mixed in a mortar at a mass ratio of 70:27:3 to prepare a positive electrode mixture powder. A negative electrode active material and a solid electrolyte were mixed in a mortar at a mass ratio of 1:1 to prepare a negative electrode mixture powder. The lower opening of a polypropylene cylinder (opening diameter 10.5 mm, height 18 mm) with an open top and bottom was blocked with a positive electrode (made of SUS), a solid electrolyte was placed on top, and the cylinder was blocked with a negative electrode (made of SUS). A solid electrolyte layer was then formed by uniaxial pressing at 180 MPa. Next, the negative electrode was temporarily removed, and a negative electrode mixture powder was placed on the solid electrolyte layer and blocked again with the negative electrode. Thereafter, the cylinder was turned upside down, the positive electrode was temporarily removed, a positive electrode mixture powder was placed on the solid electrolyte layer, and the positive electrode was again sealed, followed by uniaxial pressing at 550 MPa to produce a solid battery having a three-layer structure of the positive electrode mixture, the solid electrolyte layer, and the negative electrode mixture.

[0106] (2) [Resistance Increase Rate and Capacity Recovery Rate After Storage at 90°C] <When Core Material Particles are NCM> A charge / discharge test was carried out as follows. Specifically, the battery was placed in an environmental tester set to an environmental temperature of 25°C for charging and discharging, and the battery was left to stand until the battery temperature reached the environmental temperature. Next, a current of 0.1 C (0.3 mA / cm ２The battery was charged at a constant current and constant potential to 4.5 V at 0.1 C, then discharged at a constant current to 2.5 V at 0.1 C, and this cycle was repeated three times. The battery was then charged to a state of charge (SOC) of 50%, and the resistance before the storage test was measured by impedance measurement. The battery was then charged at a constant current and constant potential to 4.5 V at 0.1 C, and discharged at a constant current to 2.5 V at 0.1 C, and the discharge capacity was measured. The discharge capacity at this time is referred to as the initial capacity. The battery was then charged at a constant current and constant potential to 4.5 V at 0.1 C again. The battery, which had been charged at a constant current and constant potential to 4.5 V at 0.1 C, was placed in a thermostatic chamber at 90°C and stored for 168 hours. After 168 hours, the battery was removed, returned to room temperature, and then placed in an environmental test chamber at 25°C and discharged at a constant current of 0.1 C to 2.5 V. Thereafter, the battery was charged at a constant current and constant potential at 0.1 C to 4.5 V, and then discharged at a constant current of 0.1 C to 2.5 V, and the discharge capacity was measured. The discharge capacity at this time is referred to as the recovered capacity. After charging until the SOC reached 50%, the resistance value after the storage test was measured by impedance measurement. The reaction resistance increase rate after storage at 90°C was calculated using the following formula: Reaction resistance increase rate after storage at 90°C (%) = {(resistance value after storage test) - (resistance value before storage test)} / (resistance value before storage test) × 100. The recovered capacity relative to the initial capacity was calculated, and this value was used as the capacity recovery rate. Specifically, the capacity recovery rate was calculated using the following formula: Capacity recovery rate (%) = {(recovered capacity) / (initial capacity)} × 100

[0107]

[0108] As is clear from the results shown in Table 1, the solid state batteries manufactured using the active material containing the solid electrolyte obtained in the Examples in the coating layer are less likely to increase in reaction resistance and have a higher capacity recovery rate than the solid state batteries of the Comparative Examples, even when stored in a charged state at high temperatures. Furthermore, as is clear from the X-ray diffraction chart shown in Figure 1, the solid state batteries manufactured using the active material containing the solid electrolyte obtained in the Examples in the coating layer are less likely to increase in reaction resistance and have a higher capacity recovery rate than the solid state batteries of the Comparative Examples.

[0109] As described above in detail, according to the present invention, even when a solid-state battery is stored in a charged state in a high-temperature environment, it is possible to suppress a decrease in the recovery capacity of the solid-state battery and to suppress an increase in the resistance of the solid-state battery.

Claims

1. A solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X), wherein the molar ratio of halogen (X) to phosphorus (P) is less than 1.2, and the molar ratio of oxygen (O) to phosphorus (P) is greater than 0.001 and less than 1.0, and wherein the X-ray diffraction pattern measured by an X-ray diffractometer using CuKα radiation has diffraction peaks at 2θ=15.4°±1° and 2θ=17.8°±1°.

2. In the X-ray diffraction pattern, the integrated intensity of the diffraction peak observed at 2θ = 15.4° ± 1° is defined as I Ａ The integrated intensity of the diffraction peak observed at 2θ = 17.8° ± 1° is defined as I Ｂ When the integrated intensity of the diffraction peak observed at 2θ = 25.3° ± 1° is expressed as I Ｃ The integrated intensity of the diffraction peak observed at 2θ = 29.7° ± 1° is defined as I Ｄ When this is done, I Ａ / I Ｂ The value of is 0.70 or more, and I Ｃ / I Ｄ The solid electrolyte according to claim 1, wherein the value of is 0.91 or less.

3. Volume cumulative particle size D at 50% cumulative volume by laser diffraction scattering particle size distribution measurement method ５０ 3. The solid electrolyte according to claim 2, wherein the X-ray diffraction pattern has a half-width of a diffraction peak observed at 2θ=29.7°±1° of 0.3° or less.

4. The solid electrolyte according to claim 1 or 2, which has diffraction peaks at 2θ=22.0°±0.5° and 2θ=22.9°±0.5° in the X-ray diffraction pattern.

5. An active material having a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the coating layer contains a solid electrolyte including a crystalline phase having an argyrodite-type crystal structure, wherein the solid electrolyte contains lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and a halogen (X), and wherein the molar ratio of oxygen (O) to phosphorus (P) is greater than 0.001 and less than 1.

0.

6. The active material according to claim 5, wherein the core particles contain at least one selected from the group consisting of lithium transition metal composite oxides having a layered rock salt structure, lithium transition metal composite oxides having a spinel structure, and phosphate compounds having an olivine structure.

7. The active material according to claim 5 or 6, wherein the molar ratio of halogen (X) element to phosphorus (P) element in the solid electrolyte is less than 1.

2.

8. The active material according to claim 5 or 6, wherein the ratio of the coating layer to the active material is 0.1% by mass or more and 10% by mass or less.

9. An electrode mixture comprising the solid electrolyte according to claim 1 or the active material according to claim 5, and a conductive material.

10. The electrode mixture according to claim 9, comprising the active material according to claim 5, the conductive material, and a solid electrolyte, wherein the molar ratio of halogen (X) element to phosphorus (P) element is 1.2 or more.

11. An electrode layer comprising the electrode mixture according to claim 9 and a binder.

12. A solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer contains the electrode mixture according to claim 9.

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