Active material particles, electrode, electricity storage element, all-solid-state secondary battery, method for producing active material particles, and electricity storage device

Abstract

The active material particles according to one aspect of the present invention has an active material base material and a coating layer coating at least a part of the surface of the active material base material, the coating layer containing niobium atoms and phosphorus atoms, the amount of the phosphorus atoms contained in the coating layer being more than 0 mol% and 80 mol% or less of the total amount of the niobium atoms and the phosphorus atoms contained in the coating layer.

Description

[Technical Field]

[0001] The present invention relates to active material particles (hereinafter also referred to as a positive electrode active material for an all-solid-state secondary battery, or simply as an active material), an electrode (hereinafter also referred to as an electrode for an all-solid-state secondary battery), an electricity storage element, an all-solid-state secondary battery (hereinafter also referred to as an all-solid-state battery), a method for producing active material particles, and an electricity storage device. [Background technology]

[0002] Due to their high energy density, lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. The lithium ion secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring lithium ions between the electrodes. Capacitors such as lithium ion capacitors are also widely used as energy storage devices other than lithium ion secondary batteries. Furthermore, because the electrolyte of currently available lithium ion secondary batteries contains a flammable organic solvent, care must be taken in storage and handling not only during their service life but also after the end of their life. For these reasons, energy storage devices using a solid electrolyte as a non-aqueous electrolyte, such as all-solid-state batteries, have also been developed.

[0003] Conventionally, various active material particles whose surfaces are coated with oxides or the like having lithium ion conductivity have been developed as active materials particularly suitable for use in all-solid-state batteries. Patent Document 1 describes a composite positive electrode active material for a sulfide all-solid-state lithium battery, in which the surfaces of secondary particles of a positive electrode active material having an olivine structure are coated with lithium niobate.

[0004] In Example 1 of Patent Document 2, "In a dry nitrogen atmosphere, 8 mg of ethoxylithium (manufactured by Kojundo Chemical Co., Ltd.) was dissolved in 370 ml of dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) having a water content of 0.005% by weight or less. Next, 48 mg of pentaethoxyniobium (manufactured by Kojundo Chemical Co., Ltd.) was dissolved and stirred thoroughly. After confirming that no precipitate was present, a precursor solution was obtained. Next, as a pretreatment, lithium nickel cobalt manganese oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 500 g of a cathode active material (LiCoO2, manufactured by Nichia Corporation) was vacuum-dried (120°C, 10 hours) in advance. Then, using a tumbling fluidized bed coater (manufactured by Powrex Corporation), the precursor solution was applied to the cathode active material in a dry nitrogen atmosphere (dew point temperature: -80°C or lower). Next, 50 g of the cathode active material coated with the precursor solution was placed in an alumina crucible and heat-treated (400°C, 30 minutes) in a muffle furnace in a dry air atmosphere (dew point temperature: -50°C or lower), forming a reaction suppression layer and obtaining a composite cathode active material. (Paragraph

[0088] ) The same document also states, in Example 2, that "a composite cathode active material was prepared in the same manner as in Example 1, except that lithium cobalt oxide (LiCoO2, manufactured by Nichia Corporation) was used as the cathode active material." (Paragraph

[0089] ) Furthermore, the document states that the composite positive electrode active materials obtained in Examples 1 and 2 have a reaction inhibitor layer formed on the surface of the positive electrode active material, and that the reaction inhibitor layer contains a niobate compound and carbonaceous matter (paragraph

[0094] ).

[0005] In Example 4 of Patent Document 3, "0.60 g of lithium hydroxide and 0.614 g of lithium fluoride were dissolved in 19.6 g of Nb hydroxide slurry (containing 9.6 wt % of Nb hydroxide) to prepare a surface treatment solution." and "This surface treatment solution was used to prepare a lithium-containing composite oxide (LiCo 0.2 Ni 0.6 Mn 0.2The document also states that "the positive electrode active materials (samples) prepared in the examples and comparative examples were used as the positive electrode active materials, graphite (Gr) powder was used as the negative electrode active material, and a powder of the composition formula: Li was used as the solid electrolyte powder." 5.8 PS 4.8 Cl 1.2 "," "The positive electrode mixture powder was prepared by mixing the positive electrode active material (sample) produced in the Examples and Comparative Examples, the solid electrolyte powder, and the conductive material (acetylene black) powder in a mortar in a ratio of 60:37:3."," 14.5 mg of the positive electrode mixture powder was filled into the insulating cylinder (φ9 mm) of a sealed cell and uniaxially molded at 500 MPa to produce a positive electrode mixture powder pellet, and the obtained positive electrode pellet was transferred into the insulating cylinder (φ10.5 mm) of a sealed cell, and 100 mg of solid electrolyte powder was filled on the positive electrode pellet. Next, after uniaxial molding at 184 MPa together with the positive electrode mixture pellet, 18 mg of graphite (Gr) powder was filled on the solid electrolyte, and uniaxial molding was performed at 551 MPa and tightened with a pressure screw. "The all-solid-state lithium secondary battery was fabricated by incorporating the all-solid-state lithium secondary battery cell into an environmental test chamber maintained at 25°C and connecting it to a charge-discharge measuring device. The battery characteristics were evaluated by placing the all-solid-state lithium secondary battery cell in an environmental test chamber maintained at 25°C and connecting it to a charge-discharge measuring device. At this time, charging was performed by CC-CV mode with an upper limit voltage of 4.5 V, and discharging was performed by CC mode with a lower limit voltage of 2.5 V." "Charging and discharging were repeated at 0.1 C from the first to third cycles, charging at 0.2 C and discharging at 2.0 C in the fourth cycle, and charging and discharging at 0.1 C from the fifth to fifty-first cycles." and "The initial charge-discharge efficiency was expressed as the quotient obtained by dividing the discharge capacity in the first cycle by the charge capacity in the first cycle" (paragraphs

[0061] to

[0064] ). Table 1 of the same document also states that the positive electrode active material of Example 4 has a surface layer of an amorphous LiNbO compound, and the mass ratio of F to Nb is 2866.0 × 10 -4 and that the initial charge-discharge efficiency of a battery made using the positive electrode active material is 84% ​​(paragraph

[0065] ). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-91913 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-37950 [Patent Document 3] WO2019 / 035418 Summary of the Invention [Problem to be solved by the invention]

[0007] Even in energy storage devices using conventional active material particles surface-coated with lithium niobate or the like, the capacity retention rate after charge-discharge cycling is insufficient. Furthermore, all-solid-state secondary batteries are required to have high initial charge-discharge efficiency.

[0008] The present invention has been made in light of the above circumstances, and its objects are to provide active material particles that can increase the capacity retention rate of an electricity storage element after charge-discharge cycling, an electrode and electricity storage element using such active material particles, and a method for producing such active material particles, as well as to provide a positive electrode active material that can provide an all-solid-state secondary battery with high initial charge-discharge efficiency, an electrode for an all-solid-state secondary battery using such positive electrode active material, and an all-solid-state secondary battery using such an electrode.Furthermore, it is an object of the present invention to provide an electricity storage device that uses such an electricity storage element or all-solid-state secondary battery. [Means for solving the problem]

[0009] An active material particle according to one aspect of the present invention comprises an active material base material (hereinafter also referred to as base material) and a coating layer (hereinafter also referred to as surface layer) that covers at least a portion of the surface of the active material base material, the coating layer containing niobium atoms and phosphorus atoms, and the content of the phosphorus atoms relative to the total content of the niobium atoms and the phosphorus atoms in the coating layer is more than 0 mol% and not more than 80 mol%.

[0010] The positive electrode active material for an all-solid-state secondary battery according to another aspect of the present invention is composed of a base material capable of occluding and releasing lithium ions, and a surface layer that exists on the surface of the base material, contains each element of lithium, niobium, oxygen, and halogen, and satisfies 0 < c ≤ 1.0 when the ratio of the total molar number of the halogen to the molar number of the niobium is c, and is crystalline.

[0011] The electrode according to another aspect of the present invention contains the active material particles according to one aspect of the present invention or the positive electrode active material for an all-solid-state secondary battery according to one aspect of the present invention.

[0012] The power storage element according to another aspect of the present invention includes the electrode according to one aspect of the present invention.

[0013] The all-solid-state secondary battery according to another aspect of the present invention includes the electrode according to one aspect of the present invention.

[0014] The method for manufacturing active material particles according to one aspect of the present invention includes coating at least a part of the surface of a particulate active material base material with a coating agent containing niobium atoms and phosphorus atoms, and heat-treating the active material base material coated with the coating agent in this order. The content of the phosphorus atoms in the coating agent is more than 0 mol% and 80 mol% or less with respect to the total content of the niobium atoms and the phosphorus atoms.

[0015] The power storage device according to another aspect of the present invention includes two or more power storage elements, and includes one or more of the power storage element according to one aspect of the present invention or the all-solid-state secondary battery according to one aspect of the present invention.

Advantages of the Invention

[0016] According to one aspect of the present invention, it is possible to provide active material particles that can improve the capacity retention rate of an electricity storage element after charge-discharge cycling, an electrode and an electricity storage element using such active material particles, and a method for producing such active material particles.It is also possible to provide a positive electrode active material that can obtain an all-solid-state secondary battery with high initial charge-discharge efficiency, an electrode for an all-solid-state secondary battery using the positive electrode active material, and an all-solid-state secondary battery using the electrode.Furthermore, it is possible to provide an electricity storage device using such an electricity storage element or all-solid-state secondary battery. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view of an electricity storage element (all-solid-state secondary battery) according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an energy storage device configured by assembling a plurality of energy storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] First, an outline of the active material particles, electrode, electricity storage element, all-solid-state secondary battery, method for producing active material particles, and electricity storage device disclosed in this specification will be described.

[0019] An active material particle (a) according to one aspect of the present invention comprises an active material base material and a coating layer that coats at least a portion of the surface of the active material base material, the coating layer containing niobium atoms and phosphorus atoms, and the content of the phosphorus atoms relative to the total content of the niobium atoms and the phosphorus atoms in the coating layer is more than 0 mol % and not more than 80 mol %.

[0020] The active material particles (a) can improve the capacity retention rate of an energy storage device after charge-discharge cycles. Although the reason for this effect is unclear, it is presumed that the coating layer contains phosphorus atoms at a predetermined ratio together with niobium atoms, which improves the stability of the atomic arrangement structure, such as the crystalline structure, of the coating layer, thereby improving the stability of the coating layer.

[0021] It is preferable that the coating layer contains a composite oxide containing the niobium atoms and the phosphorus atoms. In such a case, the capacity retention rate after charge and discharge cycles of the energy storage device can be further increased due to, for example, higher stability of the coating layer.

[0022] It is preferable that the composite oxide is represented by the following formula 1. Li x Nb (1-y) P y O z A w ···1 In formula 1, A is one or more elements other than Li, Nb, P, and O. x is a number greater than 0 and less than or equal to 2. y is a number greater than 0 and less than or equal to 0.8. z is a number greater than or equal to 2 and less than or equal to 4. w is a number greater than or equal to 0 and less than or equal to 1. In such a case, the capacity retention rate after charge and discharge cycles of the energy storage device can be further increased.

[0023] It is preferable that the content of the coating layer with respect to the content of the active material base is 0.01% by mass or more and 2.0% by mass or less. In such a case, in addition to being able to further increase the capacity retention rate after charge and discharge cycles of the energy storage device, the discharge capacity, high-rate discharge performance, etc. of the energy storage device also tend to increase.

[0024] The positive electrode active material (b) for an all-solid-state secondary battery according to one aspect of the present invention includes a base material composed of a substance capable of occluding and releasing lithium ions, and a surface layer present on the surface of the base material, containing each element of lithium, niobium, oxygen, and halogen, and when the ratio of the total molar number of the halogen to the molar number of the niobium is c, it satisfies 0 < c ≤ 1.0 and has a crystalline surface layer.

[0025] According to this positive electrode active material (b) for an all-solid-state secondary battery, an all-solid-state secondary battery with high initial charge and discharge efficiency can be obtained.

[0026] Here, in the positive electrode active material (b) for an all-solid-state secondary battery, the halogen contained in the surface layer may be at least one selected from bromine and iodine.

[0027] Further, for the positive electrode active material (b) for the all-solid-state secondary battery, the surface layer has a composition formula Li a NbO b X c (where X is a halogen, and a, b, and c are real numbers satisfying 0.5 ≦ a ≦ 1.5, 2.5 ≦ b ≦ 3.5, and 0 < c ≦ 1.0, respectively) may also be represented.

[0028] The electrode according to another aspect of the present invention contains the active material particles (a) according to one aspect of the present invention or the positive electrode active material (b) for the all-solid-state secondary battery according to one aspect of the present invention. Since the electrode contains the active material particles according to one aspect of the present invention, the capacity retention rate after the charge-discharge cycle of the power storage element can be increased. Alternatively, according to the electrode, an all-solid-state secondary battery with high initial charge-discharge efficiency can be obtained.

[0029] [[ID=I5]]The power storage element according to another aspect of the present invention includes the electrode according to one aspect of the present invention. Since the power storage element includes an electrode containing the active material particles (a) according to one aspect of the present invention, the capacity retention rate after the charge-discharge cycle is high.

[0030] The all-solid-state secondary battery according to another aspect of the present invention includes the electrode according to one aspect of the present invention. The all-solid-state secondary battery has high initial charge-discharge efficiency.

[0031] The manufacturing method of the active material particles (a) according to one aspect of the present invention includes coating at least a part of the surface of the particulate active material base material with a coating agent containing niobium atoms and phosphorus atoms, and heat-treating the active material base material coated with the coating agent in this order. The content of the phosphorus atoms in the coating agent with respect to the total content of the niobium atoms and the phosphorus atoms is more than 0 mol% and 80 mol% or less.

[0032] According to the manufacturing method, active material particles capable of increasing the capacity retention rate after the charge-discharge cycle of the power storage element can be manufactured.

[0033] An energy storage device according to one aspect of the present invention includes two or more energy storage elements, and includes at least one of the energy storage elements according to the above-described aspect of the present invention or the all-solid-state secondary battery according to the above-described aspect of the present invention. Because the energy storage device includes the energy storage elements according to the above-described aspect of the present invention, the energy storage device has a high capacity retention rate after charge / discharge cycles. Or, because the energy storage device includes the all-solid-state secondary battery according to the above-described aspect of the present invention, the initial charge / discharge efficiency is high.

[0034] Hereinafter, an active material particle and a manufacturing method thereof, an electrode, an energy storage element, an all-solid-state secondary battery and a manufacturing method thereof, an energy storage device, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0035] <Active material particles> The active material particles according to one embodiment of the present invention (hereinafter also referred to as "the present embodiment") have an active material base material and a coating layer. The active material particles may be positive electrode active material particles used in a positive electrode or negative electrode active material particles used in a negative electrode, but are preferably positive electrode active material particles.

[0036] (active material base material) The active material matrix serves as the core of the active material. The active material matrix contains an active material. The content of the active material in the active material matrix may be, for example, 90% by mass or more, 99% by mass or more, or 99.9% by mass or more. The active material matrix may be in the form of particles or a film. When the active material matrix is ​​in the form of particles, only particles composed of one of the active materials may be used, or a mixture of two or more particles composed of different active materials may be used. The active material matrix may be particles consisting essentially of the active material alone, or may be particles consisting of the active material alone. The active material matrix may be primary particles consisting of a single crystal, or secondary particles formed by aggregation of primary particles. When the active material particles according to one embodiment of the present invention are positive electrode active material particles, the active material is a positive electrode active material. When the active material particles according to one embodiment of the present invention are negative electrode active material particles, the active material is a negative electrode active material.

[0037] The positive electrode active material can be appropriately selected from known positive electrode active materials commonly used in lithium ion secondary batteries and all-solid-state batteries. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ)Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. Among these substances, lithium transition metal composite oxides having an α-NaFeO2 crystal structure and lithium transition metal composite oxides having a spinel crystal structure are preferred because they have low interfacial resistance with the surface layer described below.

[0038] As the positive electrode active material, a lithium transition metal composite oxide is preferred, more preferably a lithium transition metal composite oxide containing at least one of nickel, cobalt, and manganese, even more preferably a lithium transition metal composite oxide containing at least two of nickel, cobalt, and manganese, and even more preferably a lithium transition metal composite oxide containing nickel, cobalt, and manganese. This lithium transition metal composite oxide preferably has an α-NaFeO2-type crystal structure. Use of such a lithium transition metal composite oxide can increase energy density, etc. Among these, lithium transition metal composite oxides having an α-NaFeO2-type crystal structure are more preferred because they allow all-solid-state secondary batteries with excellent output characteristics to be obtained at low cost. Among these, lithium transition metal composite oxides having an α-NaFeO2-type crystal structure containing cobalt are particularly preferred because they allow all-solid-state secondary batteries with even better output characteristics to be obtained.

[0039] The lithium transition metal composite oxide is preferably a compound represented by the following formula 2. Li 1+α Me 1-α O2···2 In formula 2, Me is a metal (excluding Li) including at least one of Ni, Co, and Mn, and 0≦α<1.

[0040] In formula 2, Me is preferably substantially composed of the three elements Ni, Co, and Mn, although Me may contain other metals.

[0041] From the viewpoint of achieving a larger electric capacity, the preferred contents (composition ratios) of the constituent elements in the compound represented by formula 2 are as follows: Note that the molar ratio is equal to the atomic ratio.

[0042] In formula 2, the lower limit of the molar ratio of Ni to Me (Ni / Me) is preferably 0.1, and in some cases, 0.2, 0.3, or 0.4 is more preferable, while the upper limit of this molar ratio (Ni / Me) is preferably 0.9, and in some cases, 0.8, 0.7, or 0.6 is more preferable.

[0043] In formula 2, the lower limit of the molar ratio of Co to Me (Co / Me) is preferably 0.05, and in some cases, 0.1 or 0.2 is more preferable, while the upper limit of this molar ratio (Co / Me) is preferably 0.7, and in some cases, 0.5, 0.4, or 0.3 is more preferable.

[0044] In formula 2, the lower limit of the molar ratio of Mn to Me (Mn / Me) is preferably 0.05, and in some cases, 0.1 or 0.2 is more preferable, while the upper limit of this molar ratio (Mn / Me) is preferably 0.6, and in some cases, 0.5, 0.4, or 0.3 is more preferable.

[0045] In formula 2, the upper limit of the molar ratio of Li to Me (Li / Me), ie, (1+α) / (1−α), is preferably 1.6, and in some cases is more preferably 1.4 or 1.2.

[0046] The composition ratio of the lithium transition metal composite oxide refers to the composition ratio when the device is fully discharged using the following method. First, the storage element is discharged at a constant current of 0.05 C to the lower limit voltage for normal use. Then, the device is disassembled, the positive electrode is removed, and a test battery is assembled with metallic Li as the counter electrode. The positive electrode potential is measured at a discharge current of 10 mA per 1 g of positive electrode active material until the positive electrode potential reaches 3.0 V vs. Li / Li. +The positive electrode is then fully discharged by discharging at a constant current until the positive electrode reaches a fully discharged state. The device is then disassembled again and the positive electrode is removed. Dimethyl carbonate is used to thoroughly wash away any components (electrolyte, etc.) adhering to the removed positive electrode, and the electrode is dried under reduced pressure at room temperature for 24 hours, after which the lithium transition metal composite oxide, the active material for the positive electrode, is extracted. The extracted lithium transition metal composite oxide is then subjected to measurement. The entire process from disassembling the energy storage device to preparing the sample for measurement is carried out in an argon atmosphere with a dew point of -60°C or below.

[0047] Suitable lithium transition metal composite oxides include, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 3 / 5 Co 1 / 5 Mn 1 / 5 O2, LiNi 1 / 2 Co 1 / 5 Mn 3 / 10 O2, LiNi 1 / 2 Co 3 / 10 Mn 1 / 5 O2, LiNi 8 / 10 Co 1 / 10 Mn 1 / 10 Examples include O2.

[0048] The negative electrode active material can be appropriately selected from known negative electrode active materials commonly used in lithium ion secondary batteries and all-solid-state batteries. Materials capable of absorbing and releasing lithium ions are typically used as the negative electrode active material. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples include titanium-containing oxides such as TiNbO, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Of these materials, graphite and non-graphitic carbon are preferred.

[0049] "Graphite" refers to the graphite that has an average lattice spacing (d 002) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0050] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0051] Here, the "discharged state" of a carbon material refers to a state in which the carbon material, which is a negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, in a single-electrode battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic Li as a counter electrode, this state refers to a state in which the open circuit voltage is 0.7 V or higher.

[0052] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0053] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0054] The average particle size of the active material base material can be, for example, 0.01 μm or more and 100 μm or less, and may be 0.01 μm or more and 100 μm or less. The lower limit of the average particle size of the active material base material may be 0.1 μm or may be 1 μm. The upper limit of the average particle size of the active material base material may be 20 μm or may be 5 μm. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the active material base material to be equal to or greater than the above lower limit, the active material base material can be easily manufactured or handled. By setting the average particle size of the active material base material to be equal to or less than the above upper limit, the decrease in battery capacity during high-rate discharge can be suppressed. When the negative electrode active material is a metal such as metallic Li, the active material base material may be in the form of a foil. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%, based on the particle size distribution measured by laser diffraction / scattering in accordance with JIS-Z-8825 (2013) for a diluted solution of particles diluted with a solvent.

[0055] To obtain an active material base material with a predetermined particle size, a pulverizer, a classifier, or the like is used. Examples of pulverization methods include those using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow jet mill, or a sieve. Wet pulverization in the presence of water or an organic solvent such as hexane can also be used. As a classification method, a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

[0056] (covering layer) The coating layer covers at least a portion of the surface of the active material base material. The coating layer preferably covers 50% or more of the surface of the active material base material, more preferably 70% or more, and even more preferably 90% or more, and even more preferably 95% or more. By sufficiently covering the surface of the active material base material with the coating layer, it is possible to further increase the capacity retention rate of the energy storage element after charge-discharge cycles.

[0057] The coating layer of the active material particles (a) according to one embodiment of the present invention contains niobium atoms and phosphorus atoms. The content of phosphorus atoms (P / (Nb+P)) relative to the total content of niobium atoms and phosphorus atoms in the coating layer is more than 0 mol% and not more than 80 mol%. The lower limit of the content of phosphorus atoms (P / (Nb+P)) relative to the total content of niobium atoms and phosphorus atoms is preferably 1 mol%, more preferably 5 mol%, even more preferably 10 mol%, and in some cases even more preferably 15 mol%, 25 mol%, or 35 mol%. By setting the content of phosphorus atoms to the above-mentioned lower limit or more, the capacity retention rate of the energy storage device after charge-discharge cycling can be further improved. On the other hand, the upper limit of the content of phosphorus atoms (P / (Nb+P)) relative to the total content of niobium atoms and phosphorus atoms is preferably 60 mol%, and in some cases even more preferably 40 mol%, 30 mol%, 20 mol%, or 15 mol%. By setting the content of phosphorus atoms to the above upper limit or less, the discharge capacity, charge / discharge efficiency, high-rate discharge performance, and the like of the energy storage element tend to be improved.

[0058] The coating layer preferably contains oxygen atoms in addition to niobium atoms and phosphorus atoms. The niobium atoms and phosphorus atoms are preferably present in the coating layer in the form of a composite oxide containing both of these atoms. That is, the coating layer preferably contains a composite oxide containing niobium atoms and phosphorus atoms.

[0059] The coating layer preferably further contains lithium atoms. The inclusion of lithium atoms in the coating layer improves the lithium ion conductivity of the coating layer. The coating layer preferably contains a composite oxide containing niobium atoms, phosphorus atoms, and lithium atoms. The coating layer may contain one or more oxides or composite oxides, and may further contain other compounds. The total content of one or more oxides and composite oxides in the coating layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 99% by mass or more. The coating layer may be a layer of one or more oxides and composite oxides. Compounds other than one or more oxides and composite oxides that may be contained in the coating layer include nitrides, sulfides, halides, etc.

[0060] The composite oxide contained in the coating layer is preferably represented by the following formula 1. Li x Nb (1-y) P y O z A w 1 In formula 1, A is one or more elements other than Li, Nb, P, and O. x is a number greater than 0 and equal to or less than 2. y is a number greater than 0 and equal to or less than 0.8. z is a number greater than 2 and equal to or less than 4. w is a number greater than 0 and equal to or less than 1.

[0061] Examples of A in formula 1 include typical nonmetallic elements such as B, C, N, S, F, Cl, Br, and I; typical metallic elements such as Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, and W.

[0062] In formula 1, x is preferably 0.5 or more and 1.5 or less, more preferably 0.8 or more and 1.2 or less, and even more preferably 1. When x is within the above range, the lithium ion conductivity of the coating layer becomes good.

[0063] In formula 1, the lower limit of y is preferably 0.01, more preferably 0.05, more preferably 0.1, and in some cases even more preferably 0.15, 0.25, or 0.35. By setting y to the above-mentioned lower limit or more, the capacity retention rate of the energy storage element after charge / discharge cycling can be further increased. The upper limit of y is preferably 0.6, and in some cases even more preferably 0.4, 0.3, 0.2, or 0.15. By setting y to the above-mentioned upper limit or less, the discharge capacity, charge / discharge efficiency, high-rate discharge performance, etc. of the energy storage element tend to be improved.

[0064] In formula 1, z is preferably 2.5 or more and 3.5 or less, more preferably 2.8 or more and 3.2 or less, and even more preferably 3. When z is within the above range, the structure of the oxide is stabilized, and the capacity retention rate of the energy storage element after charge-discharge cycling can be further increased.

[0065] In formula 1, w is preferably 0.5 or less, more preferably 0.2 or less, even more preferably 0.1 or less, and even more preferably 0. When w is equal to or less than the upper limit, the stability of the oxide structure is increased, and the capacity retention rate of the energy storage element after charge-discharge cycling can be further increased.

[0066] The oxide or composite oxide contained in the coating layer preferably has a crystalline structure, which increases the stability of the coating layer and thereby increases the capacity retention rate of the energy storage element after charge-discharge cycling.

[0067] The oxide or composite oxide contained in the coating layer may contain an amorphous portion, or the oxide contained in the coating layer may be composed solely of amorphous portions.

[0068] The content of the coating layer with respect to the content of the active material base material is preferably 0.01% by mass or more and 2.0% by mass or less. The lower limit of the content of the coating layer with respect to the content of the active material base material is more preferably 0.1% by mass, further preferably 0.3% by mass, and may be even more preferably 0.4% by mass, 0.6% by mass or 0.8% by mass. By setting the content of the coating layer to be not less than the above lower limit, the capacity retention rate after charge and discharge cycles of the power storage element tends to be further increased. The upper limit of the content of the coating layer with respect to the content of the active material base material is more preferably 1.6% by mass, and further preferably 1.2% by mass. By setting the content of the coating layer to be not more than the above upper limit, the discharge capacity, charge and discharge efficiency, high rate discharge performance, etc. of the power storage element tend to be increased.

[0069] The average particle size of the active material particles can be, for example, 0.01 μm or more and 100 μm or less. The lower limit of the average particle size of the active material particles may be 0.1 μm or 1 μm. The upper limit of the average particle size of the active material particles may be 20 μm or 5 μm.

[0070] On the surface of the base material included in the positive electrode active material (b) for all-solid-state secondary batteries according to an embodiment of the present invention, there is a surface layer containing each element of lithium, niobium, oxygen, and halogen. This surface layer satisfies 0 < c ≤ 1.0 when the ratio of the total molar number of halogen to the molar number of niobium is c, and is crystalline.

[0071] This surface layer allows for an all-solid-state secondary battery with high initial charge-discharge efficiency to be obtained. This is presumably due to the following mechanism of action. In an all-solid-state secondary battery, as described above, the positive electrode active material and the solid electrolyte come into contact. If the positive electrode active material has a surface layer, the surface layer comes into solid-solid contact with the solid electrolyte. When charge-discharge is performed in this state, a substitution reaction may occur between the components of the surface layer and the components of the solid electrolyte. The irreversible capacity caused by this substitution reaction reduces the initial charge-discharge efficiency. However, if the surface layer contains lithium, niobium, oxygen, and a halogen and is crystalline, it is structurally more stable than an amorphous material, and therefore the substitution reaction is less likely to occur. As a result, the irreversible capacity is reduced, and the initial charge-discharge efficiency is thought to be improved.

[0072] The effect of the surface layer in improving the initial charge-discharge efficiency is particularly pronounced when an all-solid-state secondary battery is formed by combining a sulfide solid electrolyte (described later) with a cathode active material including a base material containing oxygen as a constituent element. It is known that substitution reactions between oxygen in the cathode active material and sulfur in the solid electrolyte are likely to occur in such all-solid-state secondary batteries. Therefore, by providing a crystalline surface layer containing lithium, niobium, oxygen, and a halogen, the surface layer at the interface with the solid electrolyte is structurally stable, significantly suppressing the substitution reaction and significantly improving the initial charge-discharge efficiency. This effect of improving the initial charge-discharge efficiency is particularly pronounced when a sulfide solid electrolyte is combined with a base material composed of a lithium transition metal composite oxide, and is even more pronounced when a sulfide solid electrolyte is combined with a base material composed of a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, and is even more pronounced when a sulfide solid electrolyte is combined with a base material composed of a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure and containing cobalt as a transition metal element.

[0073] Here, whether the coating layer or surface layer is crystalline can be confirmed by the following procedure: A thin film sample containing an active material is prepared and observed under a transmission electron microscope (TEM). Electron diffraction of the coating layer or surface layer of the active material is obtained, and the presence or absence of diffraction spots is confirmed. If diffraction spots can be observed, the coating layer or surface layer is determined to be crystalline. When preparing the above-mentioned thin flake sample, if the active material to be measured is collected by disassembling the energy storage element or all-solid-state secondary battery, the sample is prepared by the following method. The energy storage element or all-solid-state secondary battery is discharged at a constant current of 0.05 C to the lower limit voltage for normal use in a 25°C environment. Next, the energy storage element or all-solid-state secondary battery is disassembled, and the electrode body is removed. Next, fragments containing the active material are collected from the removed electrode body. Next, the portion of the collected fragment containing the active material is processed into a thin flake sample using a focused ion beam (FIB) device and subjected to TEM observation.

[0074] However, if the active material is manufactured by applying a coating agent containing niobium and phosphorus atoms or a solution containing lithium, niobium, and a halogen to a base material and then heating the applied active material, and the manufacturing conditions are known and the raw materials for manufacturing the active material are available, the coating layer or surface layer may be determined to be crystalline by the following procedure. First, a solution prepared using the same procedure as the coating agent or solution to be applied to the base material is heated under the same conditions as when the active material was manufactured to obtain a sample powder. The obtained sample powder is then subjected to X-ray diffraction measurement. If peaks due to the crystalline structure are observed in the obtained X-ray diffraction pattern, the coating layer or surface layer is determined to be crystalline.

[0075] X-ray diffraction measurement is performed according to the following procedure. First, the sample powder is filled into a sample holder for X-ray diffraction measurement. Then, powder X-ray diffraction measurement is carried out using an X-ray diffractometer ("MiniFlex II" manufactured by Rigaku). The radiation source is CuKα ray, the tube voltage is 30 kV, the tube current is 15 mA, and the diffracted X-ray is detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2) after passing through a Kβ filter with a thickness of 30 μm. The sampling width is 0.01°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

[0076] The ratio of the total number of moles of halogen to the number of moles of niobium in the surface layer, that is, the value of c above, is 1.0 or less. By the value of c being below the above upper limit, oxygen in the surface layer can be made in a stable state. From the point of further improving the stability of oxygen in the surface layer, the value of c is preferably 0.8 or less, more preferably 0.5 or less, and even more preferably 0.3 or less. On the other hand, from the point of making the suppressing effect of the substitution reaction between oxygen in the above-mentioned surface layer and components in the solid electrolyte sufficient, the value of c is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. Also, for these reasons, the value of c is preferably 0.01 or more and 0.8 or less, more preferably 0.05 or more and 0.5 or less, and even more preferably 0.1 or more and 0.3 or less.

[0077] The surface layer has a composition formula Li a NbO b X c (where X is a halogen, and a, b, and c are real numbers satisfying 0.5 ≤ a ≤ 1.5, 2.5 ≤ b ≤ 3.​​​The formula of the surface layer is determined by the following procedure. The positive electrode active material is quantitatively analyzed using an inductively coupled plasma atomic emission spectroscopy (ICP-AES) analyzer or an X-ray photoelectron spectroscopy (XPS) analyzer to confirm the constituent elements and composition of the positive electrode active material. For elements that can be quantified by ICP-AES, their content is determined based on the ICP-AES measurement results. When performing the ICP-AES analysis, the positive electrode active material is completely dissolved in an acidic solution using a microwave decomposition method, and the analysis sample is prepared. The crystal structure of the surface layer is then confirmed by TEM observation. If the surface layer is amorphous, the positive electrode active material is heat-treated to crystallize the surface layer, and the crystal structure of the surface layer is then confirmed. The formula of the surface layer is estimated from the obtained information, and this formula is used as the formula of the surface layer. When the positive electrode active material to be subjected to quantitative elemental analysis is extracted by disassembling an all-solid-state secondary battery, it is prepared as follows. First, the all-solid-state secondary battery is discharged at a constant current of 0.05 C to the lower limit voltage during normal use. Next, the all-solid-state secondary battery is disassembled and the electrode body is removed. The surfaces of the electrode body and the electrode are observed, and if it is confirmed that the positive electrode active material layer contains particulate positive electrode active material and that the removed electrode body contains a solid electrolyte, the electrode body is immersed in a solvent that dissolves only solid electrolytes, such as ethanol or ion-exchanged water, to remove the solid electrolyte. Next, the positive electrode active material layer is immersed in a solvent that dissolves only binders, such as butyl butyrate, to remove the binder, and the conductive agent and positive electrode active material are removed. Next, decantation is performed using a solvent such as ion-exchanged water to separate the conductive agent and the positive electrode active material, and the resulting positive electrode active material is used as a measurement sample. When the surface of the electrode is observed and it is confirmed that the positive electrode active material layer contains a film of the positive electrode active material, the electrode is used as a measurement sample either as is or cut into an appropriate size. Note that the surface on which the positive electrode active material layer is formed is used as the measurement surface for the sample subjected to XPS analysis.

[0079] The halogen contained in the surface layer is preferably at least one selected from bromine and iodine. When the halogen is one of the above, an all-solid-state secondary battery with higher initial charge-discharge efficiency can be obtained. This is presumably because the inclusion of the halogen makes the surface layer structurally more stable, and the substitution reaction with the solid electrolyte components during charge-discharge of the all-solid-state secondary battery is further suppressed.

[0080] The amount of the surface layer is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more, relative to the base material. By setting the amount of the surface layer at or above the lower limit, the chemical or electrochemical stability of the positive electrode active material can be improved and unintended reactions can be suppressed. On the other hand, the amount of the surface layer is preferably 0.70% by mass or less, and more preferably 0.65% by mass or less, relative to the base material. By setting the amount of the surface layer at or below the upper limit, a decrease in battery capacity during high-rate discharge can be suppressed when the all-solid-state secondary battery is formed. For these reasons, the amount of the surface layer is preferably 0.05% by mass or more and 0.70% by mass or less, and more preferably 0.10% by mass or more and 0.65% by mass or less, relative to the base material.

[0081] In the positive electrode active material (b) for an all-solid-state secondary battery according to this embodiment, the surface layer is preferably present so as to cover the entire surface of the base material. However, even if there are portions where the base material is exposed, if the area of ​​the exposed portions occupies a relatively small proportion of the total surface area of ​​the base material and the exposed portions are not unevenly distributed in specific locations on the base material, the positive electrode active material (b) for an all-solid-state secondary battery will exhibit the above-mentioned effects. Furthermore, as described above, when two or more types of base material particles made of different materials are mixed and used, it is sufficient that at least one type of base material particle has a surface layer.

[0082] When the base material is particulate, the average particle size of the positive electrode active material (b) for an all-solid-state secondary battery formed of the base material and the surface layer is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material (b) to be equal to or greater than the above lower limit, the positive electrode active material can be easily manufactured or handled. By setting the average particle size of the positive electrode active material (b) to be equal to or less than the above upper limit, the decrease in battery capacity during high-rate discharge can be suppressed. Note that when a composite of the positive electrode active material (b) and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material (b).

[0083] In order to obtain the positive electrode active material (b) with a predetermined particle size, the particle size of the base material may be adjusted using a pulverizer, a classifier, etc. As the pulverizing method and the classifying method, the methods exemplified above can be used.

[0084] (Application) The active material particles (a) can be used in various types of energy storage elements, but are particularly suitable for energy storage elements using a solid electrolyte, especially all-solid-state energy storage elements. When the active material particles (a) are used in an energy storage element using a solid electrolyte, a good interface between the active material particles and the solid electrolyte is formed, and the effect of increasing the capacity retention rate after charge-discharge cycles is particularly fully exhibited. The active material particles (a) can also be applied to energy storage elements using a combination of a solid electrolyte and an electrolytic solution as the electrolyte, energy storage elements using only an electrolytic solution as the electrolyte, etc.

[0085] <Method of manufacturing active material particles> A method for producing active material particles (a) according to one embodiment of the present invention comprises, in this order: (1) coating at least a portion of the surface of a particulate active material base material with a coating agent containing niobium atoms and phosphorus atoms; and (2) heat-treating the active material base material coated with the coating agent.

[0086] The positive electrode active material (b) according to this embodiment can be suitably produced by a method in which a solution containing lithium, niobium, and a halogen element is applied to a base material, and then the base material is heated.

[0087] (1) Coating process A conventionally known active material can be used as the particulate active material base material used in this step. The particulate base material can be produced by mixing powdered raw materials in a predetermined ratio and firing the resulting mixture. The powdered raw materials used in this case may be those obtained by coprecipitation. Furthermore, a film-like base material can be produced, for example, by sputtering using a target having a predetermined composition. Specific examples and preferred examples of this active material base material are the same as the examples of the active material base material contained in the active material particles according to one embodiment of the present invention described above.

[0088] The coating agent used in the method for producing active material particles (a) contains niobium atoms and phosphorus atoms. The coating agent may be, for example, a solution composed of a solute and a solvent. Niobium atoms and phosphorus atoms are usually contained in the solute component of the coating agent. The content of phosphorus atoms relative to the total content of niobium atoms and phosphorus atoms in the coating agent is more than 0 mol % and not more than 80 mol %. The preferred range of the content of phosphorus atoms relative to the total content of niobium atoms and phosphorus atoms in the coating agent is the same as the content of phosphorus atoms relative to the total content of niobium atoms and phosphorus atoms in the coating layer described above.

[0089] The coating agent preferably further contains lithium atoms in the solute components. The coating agent can be prepared, for example, by dissolving a niobium-containing compound, a phosphorus-containing compound, and a lithium-containing compound as solutes in a solvent. The solute may be a compound containing two or more of niobium atoms, phosphorus atoms, and lithium atoms. Examples of niobium-containing compounds include niobium alkoxides such as niobium(V) ethoxide and niobium(V) methoxide, niobium acetate, and niobium hydroxide. Examples of phosphorus-containing compounds include phosphoric acid and phosphate esters. Examples of lithium-containing compounds include lithium alkoxides such as lithium ethoxide and lithium methoxide, lithium acetate, and lithium hydroxide. The mixing ratio of each component is appropriately set depending on the composition of the desired coating layer or the oxide or composite oxide that constitutes the coating layer. The solvent used in the coating agent is not particularly limited as long as it can dissolve the niobium-containing compound, phosphorus-containing compound, and lithium-containing compound, but ethanol, for example, can be used.

[0090] The solution to be applied to the base material used in the manufacturing method of the positive electrode active material (b) can be prepared, for example, by dissolving a niobium-containing compound, a halogen-containing compound, and a lithium-containing compound in a solvent. A compound containing two or more elements selected from niobium, halogen, and lithium may also be used. Examples of niobium-containing compounds include niobium alkoxides such as niobium(V) ethoxide and niobium(V) methoxide, niobium acetate, and niobium hydroxide. Examples of halogen-containing compounds include niobium halides and lithium halides. Examples of lithium-containing compounds include lithium alkoxides such as lithium ethoxide and lithium methoxide, lithium acetate, and lithium hydroxide. The mixing ratio of each component is appropriately determined depending on the desired composition of the surface layer. The solvent used in the solution is not particularly limited as long as it can dissolve the niobium-containing compound, halogen-containing compound, and lithium-containing compound, but ethanol, for example, can be used.

[0091] Coating of the active material base material surface with a coating agent or solution can be performed by conventional coating methods such as spin coating, dip coating, and tumbling fluidized coating. Among these, tumbling fluidized coating is preferred because it is easy to obtain a highly uniform coating layer. Tumbling fluidized coating is a coating method in which the active material base material is placed in a tumbling fluidized state, and the coating agent or solution is sprayed onto the active material base material in the tumbling fluidized state and then dried (solvent removal). The temperature inside the tumbling fluidized coating apparatus during tumbling fluidized coating can be, for example, 60°C or higher and 120°C or lower. Depending on the coating method, a drying step (solvent removal step) of the coating agent or solution may be performed separately from the coating step of the coating agent or solution. Furthermore, when the base material is in a film form, spin coating, bar coating, spray coating, etc. can be suitably used.

[0092] The coating process by tumbling fluidized coating or the like may be carried out in an inert gas atmosphere such as nitrogen or argon, or in the air. The amount of coating agent or solution used (coating amount) can be adjusted appropriately depending on the amount of the coating layer to be formed.

[0093] (2) Heat treatment process In this step, the active material base material coated with the coating agent or solution is heat-treated. Before the heat treatment, the coating agent or solution may be present on the surface of the active material base material in a dry state (a state in which the solvent has been removed, or a state in which only the solute remains). In the heat treatment step, the coating agent or solution may be dried (the solvent is removed). Through this heat treatment, active material particles (a) having a coating layer containing niobium atoms, phosphorus atoms, and other optional atoms are formed, or positive electrode active material (b) having a crystalline surface layer containing the elements lithium, niobium, oxygen, and halogens are obtained.

[0094] The heat treatment is preferably carried out in an oxygen-containing atmosphere, and may be carried out in air, for example. The heat treatment temperature is preferably 250°C to 550°C, more preferably 300°C to 500°C, and even more preferably 350°C to 450°C. The heat treatment time is preferably 1 minute to 10 hours, more preferably 10 minutes to 4 hours, and even more preferably 15 minutes to 2 hours.

[0095] In the method for producing the positive electrode active material (b), it is sometimes preferable to heat the base material to which the solution is attached in an air atmosphere at a temperature of 300°C to 600°C for 10 minutes to 1 hour. This causes the elements contained in the solution to react with each other to form a surface layer. It is presumed that the halogen contained in the solution contributes to the formation of a regular arrangement of atoms or ions, making the surface layer crystalline. It is sometimes preferable that the halogen is at least one selected from bromine and iodine, since this makes the surface layer structurally more stable and more likely to suppress substitution reactions with the solid electrolyte components during charging and discharging of the all-solid-state secondary battery.

[0096] <Electrode> An electrode according to one embodiment of the present invention contains the active material particles (a) according to one embodiment of the present invention or the positive electrode active material for an all-solid-state secondary battery (b) according to one aspect of the present invention. The electrode has a substrate and an active material layer disposed on the substrate directly or via an intermediate layer. The electrode may be a positive electrode or a negative electrode, but is preferably a positive electrode.

[0097] (base material) The substrate is electrically conductive. Whether or not it is "electrically conductive" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm.

[0098] When the electrode is a positive electrode, the material of the substrate (positive electrode substrate) is a metal such as aluminum, titanium, tantalum, stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor deposition film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloy include A1085, A3003, and A1N30 specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0099] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the energy storage device. The "average thickness" of the positive electrode substrate and the negative electrode substrate described below refers to the value obtained by dividing the punched mass when a substrate of a predetermined area is punched out by the true density and punched area of ​​the substrate.

[0100] When the electrode is a negative electrode, the material of the substrate (negative electrode substrate) may be a metal such as copper, nickel, stainless steel, nickel-plated steel, or aluminum, or an alloy thereof, or a carbonaceous material. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include foil, a vapor-deposited film, a mesh, and a porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or a copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0101] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the energy storage element.

[0102] (middle class) The intermediate layer is a layer disposed between the substrate and the active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the substrate and the active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0103] (active material layer) The active material layer contains active material particles according to one embodiment of the present invention. The active material layer contains optional components such as a solid electrolyte, a conductive agent, a binder, a thickener, and a filler, as needed. The active material layer may be formed from a mixture (positive electrode mixture or negative electrode mixture) containing the active material particles and the like.

[0104] When the electrode is a positive electrode, the active material layer (positive electrode active material layer) uses positive electrode active material particles as the active material particles. When the electrode is a negative electrode, the active material layer (negative electrode active material layer) uses negative electrode active material particles as the active material particles. The content of the active material particles in the active material layer is preferably 30% by mass or more and 99% by mass or less, more preferably 50% by mass or more and 98% by mass or less, even more preferably 60% by mass or more and 95% by mass or less, and in some cases even more preferably 70% by mass or more, 80% by mass or more, or 90% by mass or more. By setting the content of the active material particles within the above range, it is possible to achieve both high energy density and manufacturability of the energy storage element.

[0105] The solid electrolyte may be a conventionally known solid electrolyte, such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, an oxynitride solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a quasi-solid electrolyte, with a sulfide-based solid electrolyte being preferred.

[0106] Examples of sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S 2n (where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.) Li 10 GeP2S 12 The solid electrolyte contained in the active material layer may be the same as that contained in the separator layer, which will be described later, or may be different from this.

[0107] When the active material layer contains a solid electrolyte, the content of the solid electrolyte in the active material layer is preferably 10% by mass to 90% by mass, more preferably 20% by mass to 70% by mass, and even more preferably 25% by mass to 50% by mass. By setting the content of the solid electrolyte within the above range, the electric capacity of the storage element can be increased. When the electrode according to one embodiment of the present invention is applied to a non-aqueous electrolyte storage element, the active material layer does not need to contain a solid electrolyte.

[0108] In the active material layer, the active material particles and the solid electrolyte may form a complex. Examples of the complex of the active material particles and the solid electrolyte include a complex having a chemical or physical bond between the active material particles and the solid electrolyte, and a complex in which the active material particles and the solid electrolyte are mechanically combined. The complex is one in which the active material particles and the solid electrolyte are present within a single particle, and examples thereof include a complex in which the active material particles and the solid electrolyte are in an aggregated state, and a complex in which a coating containing the solid electrolyte is formed on at least a portion of the surface of the active material particles.

[0109] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity, and acetylene black is particularly preferred.

[0110] The content of the conductive agent in the active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent within this range, the energy density of the energy storage element can be increased.

[0111] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0112] The binder content in the active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the active material particles can be stably held.

[0113] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0114] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0115] The active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the active material particles, solid electrolyte, conductive agent, binder, thickener, and filler.

[0116] The average thickness of the active material layer is preferably 10 μm or more and 1,000 μm or less, and more preferably 30 μm or more and 500 μm or less. By setting the average thickness of the active material layer to the above lower limit or more, it is possible to obtain an energy storage device with a high energy density. By setting the average thickness of the active material layer to the above upper limit or less, it is possible to achieve miniaturization of the energy storage device. The average thickness of the active material layer is the average value of thicknesses measured at any five positions. The same applies to the average thickness of the isolation layer described below.

[0117] <Energy storage element> An all-solid-state battery (hereinafter, also referred to as an all-solid-state secondary battery or simply a secondary battery) will be specifically described below as an energy storage element according to one embodiment of the present invention. The all-solid-state secondary battery according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a separator layer, and a container for accommodating the electrode assembly. The separator layer is composed of a solid electrolyte. The electrode assembly is typically a laminated type in which multiple positive electrodes and multiple negative electrodes are stacked with separator layers interposed between them. The electrode assembly may also be a so-called "bipolar type" in which a positive electrode active material layer is formed on one side of a substrate and a negative electrode active material layer is formed on the other side. The energy storage element 10 in FIG. 1 is an all-solid-state secondary battery, a secondary battery in which a positive electrode 1 and a negative electrode 2 are arranged with a separator layer 3 interposed between them. The positive electrode 1 includes a positive electrode substrate 4 and a positive electrode active material layer 5, with the positive electrode substrate 4 being the outermost layer of the positive electrode 1. The negative electrode 2 includes a negative electrode substrate 7 and a negative electrode active material layer 6, with the negative electrode substrate 7 being the outermost layer of the negative electrode 2. 1, an anode active material layer 6, a separator 3, a cathode active material layer 5, and a cathode substrate 4 are laminated in this order on an anode substrate 7. At least one of the cathode 1 and the anode 2 in the energy storage element 10 is an electrode according to one embodiment of the present invention.

[0118] (positive electrode) The positive electrode 1 includes a positive electrode substrate 4 and a positive electrode active material layer 5 disposed directly or via an intermediate layer on the positive electrode substrate 4. In one embodiment of the present invention, when an electrode according to one embodiment of the present invention is used for the positive electrode 1, specific and preferred forms of the positive electrode substrate 4 and positive electrode active material layer 5 of the positive electrode 1 are as described above for the substrate (positive electrode substrate) and active material layer (positive electrode active material layer) provided in the electrode according to one embodiment of the present invention.

[0119] In another embodiment of the present invention, when an electrode according to one embodiment of the present invention is used as the negative electrode 2, the positive electrode 1 may be a conventionally known positive electrode. Examples of such a positive electrode 1 include a positive electrode similar to the electrode (positive electrode) according to one embodiment of the present invention described above, except that conventionally known positive electrode active material particles are used as the active material particles.

[0120] In addition to the above-described forms, the positive electrode may be in a form in which a current collecting tab is attached to a positive electrode mixture pellet containing a positive electrode active material, and optional components such as a conductive agent, a binder, a thickener, a filler, and a solid electrolyte, or in which a current collector formed of conductive fibers or a foam-type current collector is impregnated with the positive electrode mixture.

[0121] (Negative electrode) The negative electrode 2 includes a negative electrode substrate 7 and a negative electrode active material layer 6 disposed directly or via an intermediate layer on the negative electrode substrate 7. In one embodiment of the present invention, when an electrode according to one embodiment of the present invention is used for the negative electrode 2, specific and preferred forms of the negative electrode substrate 7 and negative electrode active material layer 6 of the negative electrode 2 are as described above for the substrate (negative electrode substrate) and active material layer (negative electrode active material layer) provided in the electrode according to one embodiment of the present invention.

[0122] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the negative electrode active material can be easily manufactured or handled. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the decrease in battery capacity during high-rate discharge can be suppressed. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the powder classification method can be selected from, for example, the methods exemplified for the active material particles. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of a foil.

[0123] In another embodiment of the present invention, when the electrode according to one embodiment of the present invention is used as the positive electrode 1, the negative electrode 2 may be a conventionally known negative electrode. Examples of such negative electrodes 2 include negative electrodes similar to the electrode (negative electrode) according to one embodiment of the present invention described above, except that conventionally known negative electrode active material particles are used as the active material particles. In another embodiment, the negative electrode active material layer 6 may be a layer consisting essentially of metallic lithium. In this case, the lithium content in the negative electrode active material layer 6 may be 90% by mass or more, 99% by mass or more, or even 100% by mass. The negative electrode active material layer 6 may be a metallic lithium foil or a lithium alloy foil.

[0124] (isolation layer) The separator 3 usually contains a solid electrolyte. As the solid electrolyte contained in the separator 3, the above-mentioned conventionally known solid electrolytes can be used, and examples thereof include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes. Among them, sulfide-based solid electrolytes are preferred because they have high ionic conductivity and are easily plastically deformed, which facilitates the formation of interfaces with the positive electrode active material and the negative electrode active material. The sulfide solid electrolyte is a solid electrolyte containing sulfur as a constituent element, and examples thereof include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 , Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-Li3N, Li2S-SiS2, Li2S-S iS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S 2n (where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In.) The content of the solid electrolyte in the isolation layer 3 is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and in some cases even more preferably substantially 100% by mass.

[0125] In addition to the solid electrolyte, the separator 3 may contain optional components such as a phosphate compound such as LiPO, an oxide, a halogen compound, a binder, a thickener, a filler, etc. The optional components such as the binder, the thickener, and the filler can be selected from the materials exemplified as components in the active material layer.

[0126] The average thickness of the isolating layer 3 is preferably 1 μm or more and 200 μm or less, more preferably 3 μm or more and 100 μm or less. Alternatively, it may be preferably 1 μm or more and 50 μm or less, more preferably 3 μm or more and 20 μm or less. By setting the average thickness of the isolating layer 3 to be equal to or greater than the above lower limit, it is possible to insulate the positive electrode 1 and the negative electrode 2 with high reliability. By setting the average thickness of the isolating layer 3 to be equal to or less than the above upper limit, it is possible to increase the energy density of the energy storage element 10.

[0127] <Method of manufacturing an energy storage element> The energy storage device according to one embodiment of the present invention can be manufactured by a conventionally known method. In the case of the energy storage device 10, which is the all-solid-state battery described above, for example, the manufacturing method includes (1) mixing a positive electrode active material with a solid electrolyte for a positive electrode active material layer to prepare a positive electrode mixture, (2) preparing a material for a separator layer, (3) mixing a negative electrode active material with a solid electrolyte for a negative electrode active material layer to prepare a negative electrode mixture, and (4) laminating a positive electrode, a separator layer, and a negative electrode.

[0128] (1) Positive electrode mixture preparation process In this step, a cathode mixture for forming a cathode active material layer is usually prepared. The method for preparing the cathode mixture is not particularly limited and can be appropriately selected depending on the purpose. For example, mechanical milling of the cathode mixture material, compression molding of the cathode mixture material, etc. can be mentioned. When the cathode mixture contains a mixture or composite containing cathode active material particles and a solid electrolyte, this step can include mixing the cathode active material particles and the solid electrolyte using, for example, a mechanical milling method, etc., to prepare a mixture or composite of the cathode active material particles and the solid electrolyte.

[0129] (2) Preparation of materials for the isolation layer In this step, an isolation layer material for forming an isolation layer is usually prepared. The isolation layer material can usually be a solid electrolyte. The solid electrolyte as an isolation layer material can be prepared by a conventionally known method. For example, it can be obtained by processing a predetermined material by a mechanical milling method. The isolation layer material may also be prepared by heating predetermined materials to a melting temperature or higher by a melt quenching method, melt-mixing the materials in a predetermined ratio, and then quenching. Other methods for synthesizing isolation layer materials include, for example, a solid-phase method in which the material is sintered under reduced pressure, a liquid-phase method such as solution deposition, a vapor-phase method (PLD), and sintering in an argon atmosphere after mechanical milling.

[0130] (3) Negative electrode mixture preparation process In this step, a negative electrode mixture for forming a negative electrode active material layer is usually prepared. The specific method for preparing the negative electrode mixture is the same as that for preparing the positive electrode mixture.

[0131] (4)Lamination process In this process, for example, a positive electrode having a positive electrode substrate and a positive electrode active material layer, a separator, and a negative electrode having a negative electrode substrate and a negative electrode active material layer are laminated. In this process, the positive electrode, separator, and negative electrode may be formed sequentially in this order, or vice versa; the order of forming each layer is not particularly important. For example, the positive electrode is formed by pressure molding a positive electrode substrate and a positive electrode mixture, the separator is formed by pressure molding an separator material, and the negative electrode is formed by pressure molding a negative electrode substrate and a negative electrode mixture. The positive electrode, separator, and negative electrode may be laminated by pressure molding the positive electrode substrate, the positive electrode mixture, the separator material, the negative electrode mixture, and the negative electrode substrate all at once. The positive electrode and the negative electrode may be molded in advance, and then pressure molded and laminated with the separator.

[0132] <Electricity storage device> The energy storage element or all-solid-state secondary battery according to one embodiment of the present invention can be mounted as an energy storage unit (battery module) comprising a collection of a plurality of energy storage elements or all-solid-state secondary batteries in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one energy storage element or all-solid-state secondary battery included in the energy storage unit.

[0133] An energy storage device according to one embodiment of the present invention is an energy storage device that includes two or more energy storage elements and at least one of the energy storage elements according to one embodiment of the present invention or all-solid-state secondary batteries. Fig. 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected energy storage elements 10, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects the two or more energy storage elements 10, or a bus bar (not shown) that electrically connects the two or more energy storage units 20. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of the one or more energy storage elements 10.

[0134] <Other embodiments> The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0135] In the above embodiment, the energy storage element is described as a chargeable and dischargeable all-solid-state battery. However, the type, shape, size, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries and capacitors such as electric double layer capacitors and lithium ion capacitors. For example, the energy storage element according to the present invention may include layers other than the positive electrode, separator, and negative electrode. The structures of the positive electrode, separator, and negative electrode are not limited to those described above. Furthermore, the energy storage element according to the present invention may contain a liquid in one or more of the layers. The energy storage element according to the present invention may also be a nonaqueous electrolyte storage element in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and a nonaqueous electrolyte is used as the electrolyte. [Example]

[0136] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0137] [Example 1] (Preparation of coating agent) The coating layer formed is LiNb 0.9 P 0.1 The coating agent was prepared as follows to obtain a composite oxide represented by O3. In an argon atmosphere glove box, niobium (V) ethoxide (Nb(OCH2CH3)5, Aldrich) and lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (manufactured by Aldrich) and phosphoric acid powder (manufactured by Aldrich) were added to prepare a coating agent. The amounts of niobium (V) ethoxide, lithium ethoxide solution, and phosphoric acid powder mixed were adjusted so that the molar ratio of niobium atoms, lithium atoms, and phosphorus atoms in the coating agent was 9:10:1.

[0138] (Preparation of active material particles) The particulate active material base material is LiNi, the positive electrode active material. 1 / 2 Co 1 / 5 Mn 3 / 10O2 was prepared. The surface of the active material base material was coated with a coating agent using tumbling fluidized coating, and then dried. The tumbling fluidized coating device used was the "FD-MP-micro" manufactured by Powrex. The temperature of the device's air inlet during coating was set to 100°C. The amount of coating agent applied was also adjusted so that the coating layer formed was 0.50% by mass of the active material base material. The dried active material base material coated with the coating agent was then heat-treated in an air atmosphere for 30 minutes at a temperature of 400°C to obtain active material particles. Separately, the coating agent was dried and heat-treated under the conditions described above to obtain a powder, which was then subjected to powder X-ray diffraction analysis using the method described above, and it was confirmed that the coating layer on the active material particles thus obtained was a LiNb having a crystalline structure. 0.9 P 0.1 It is believed to contain O3.

[0139] (Fabrication of energy storage element) Using the obtained active material particles, an electricity storage element (all-solid-state battery) of Example 1 was produced in the following manner. In a glove box under an argon atmosphere, the active material particles, sulfide-based solid electrolyte (Li6PS5Cl), conductive agent (acetylene black), and binder (SBR) were weighed out to a mass ratio of 66.5:28.5:2:3. First, the active material particles, sulfide-based solid electrolyte, and conductive agent were mixed in an agate mortar. Next, butyl acetate as a binder and solvent was added to this mixture, and the mixture was kneaded in a hybrid mixer to form a positive electrode paste. The resulting positive electrode paste was applied to aluminum foil (average thickness 20 μm) as a positive electrode substrate using a YBA-type baker applicator. After drying the solvent, the positive electrode active material layer had a basis weight of 15 mg cm. -2 More than 25mg cm -2 The coating was performed as follows. This was dried in a dryer in an argon atmosphere at 100°C under normal pressure for 10 minutes and then under reduced pressure for 10 minutes to form a positive electrode active material layer on the positive electrode substrate. This was punched out into a circle with a diameter of 10 mm to prepare a positive electrode for evaluation. Next, 80 mg of sulfide-based solid electrolyte (Li6PS5Cl) was inserted into a ceramic powder compactor with an inner diameter of 10 mm and pressure-molded using a uniaxial press at a pressure of 100 MPa for several seconds to form an isolation layer. After releasing the pressure, the prepared positive electrode was laminated on one side of the isolation layer with the positive electrode active material layer facing the isolation layer, and then pressed using a uniaxial press at 360 MPa for 5 minutes. After releasing the pressure, indium foil (average thickness 300 μm, diameter 8 mm, manufactured by Nilaco) and lithium foil (average thickness 300 μm, diameter 6 mm, manufactured by Honjo Metal Co., Ltd.) as a negative electrode, and SUS316 foil (manufactured by Nilaco) as a negative electrode substrate were laminated on the side opposite the laminated surface of the positive electrode, and then pressed using a uniaxial press at a pressure of 50 MPa for several seconds. The resulting product was removed from the ceramic powder compactor to obtain the energy storage element (all-solid-state battery) of Example 1.

[0140] [Examples 2 to 10, Comparative Example 1] The active material particles and energy storage elements of Examples 2 to 10 and Comparative Example 1 were produced in the same manner as in Example 1, except that the coating agent was prepared so that the composition of the coating layer and the content of the coating layer relative to the active material base material were as shown in Table 1, and the coating amount of the coating agent was adjusted.

[0141] [Rating 1] (1) Capacity confirmation test 1 For each of the obtained energy storage elements, a capacity confirmation test 1 was carried out at a temperature of 50° C. in the following manner. Constant current / constant voltage charging was performed with a charging current of 0.1 C and a charge cut-off voltage of 3.75 V. The charge was terminated when the charging current reached 0.025 C. A 10-minute rest period was then allowed. Subsequently, constant current discharging was performed with a discharging current of 0.1 C and a discharge cut-off voltage of 2.25 V. A 10-minute rest period was then allowed. Next, constant-current / constant-voltage charging was performed with a charging current of 0.1 C and a cut-off voltage of 3.75 V. The charge was terminated when the charging current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed with a discharging current of 1.0 C and a cut-off voltage of 2.25 V. The discharge capacity in the initial charge / discharge cycle (0.1C discharge capacity), the ratio of the discharge capacity to the charge capacity in the initial charge / discharge cycle (charge / discharge efficiency), and the ratio of the discharge capacity at a discharge current of 1.0C to the discharge capacity at a discharge current of 0.1C (discharge capacity ratio 1C / 0.1C) were determined. The results are shown in Table 1.

[0142] (2) Charge / discharge cycle test Next, a charge-discharge cycle test was carried out on each of the energy storage elements at a temperature of 50° C. in the following manner. Constant current / constant voltage charging was performed with a charging current of 0.2 C and a charge cut-off voltage of 3.75 V. Charging was terminated until the charging current reached 0.05 C. Subsequently, constant current discharging was performed with a discharging current of 0.2 C and a discharge cut-off voltage of 2.25 V. A 10-minute rest period was provided after each charge and discharge. This charge / discharge cycle was repeated 50 times. The capacity retention rate was calculated by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle. The measurement results are shown in Table 1.

[0143] [Table 1]

[0144] As shown in Table 1, the energy storage elements of Examples 1 to 10 have higher capacity retention rates after charge-discharge cycling than the energy storage element of Comparative Example 1. Furthermore, a comparison of Examples 2, 5, and 9, which have the same coating layer content of 0.75 mass%, for example, reveals that increasing the phosphorus atom content relative to the total amount of niobium atoms and phosphorus atoms further enhances the capacity retention rate. Meanwhile, the 0.1C discharge capacity, charge-discharge efficiency, and discharge capacity ratio 1C / 0.1C tend to increase with a lower phosphorus atom content. Regarding the coating layer content relative to the active material base material content, increasing the coating layer content tends to relatively enhance the capacity retention rate. However, when the coating layer content is increased to 1.50 mass%, as in Example 7, the capacity retention rate is not affected, but the 0.1C discharge capacity, charge-discharge efficiency, and discharge capacity ratio 1C / 0.1C tend to decrease.

[0145] [Example 11] (Preparation of the solution to be attached to the base material) The composition ratio is LiNbO 2.9 Br 0.2 The solution to be attached to the base material was prepared as follows: In a glove box under an argon atmosphere, ultra-dehydrated ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in niobium (V) ethoxide (Nb(OCH2CH3)5, Aldrich), lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (Aldrich) and lithium bromide (Aldrich) were added to prepare a solution to be attached to the base material. The amounts of niobium (V) ethoxide, lithium ethoxide solution, and lithium bromide mixed were adjusted so that the molar ratio of niobium atoms, lithium atoms, and bromine atoms in the solution to be attached to the base material was 5:5:1.

[0146] (Preparation of particulate positive electrode active material) The base material is a lithium transition metal composite oxide, LiNi, with an α-NaFeO2 type crystal structure. 0.5 Co 0.2 Mn 0.3 O2 powder was prepared. The solution to be applied to the base material was uniformly applied to the surface of the base material particles using tumbling fluidized coating. The tumbling fluidized coating device used was the "FD-MP-micro" manufactured by Powrex. The temperature of the air inlet of the device during coating was set to 140°C. The amount of solution to be applied to the base material was also adjusted so that the surface layer formed would be 0.50% by mass of the base material. Next, the base material, after drying to remove ethanol from the solution to be adhered to the base material particle surface, was heat-treated in an air atmosphere to form a surface layer, thereby obtaining positive electrode active material particles for an all-solid-state secondary battery of Example 11. The heat treatment time was 30 minutes, and the heat treatment temperature was 400°C. Note that, hereinafter, "positive electrode active material particles for an all-solid-state secondary battery" may be abbreviated simply as "active material particles." The surface layer of the obtained active material particles was confirmed to be crystalline by the method described above. That is, a solution prepared by the same procedure as the solution to be attached to the base material was heated under the same conditions as in the production of the positive electrode active material to obtain a sample powder. The obtained sample powder was then subjected to X-ray diffraction measurement. The X-ray diffraction measurement was performed by the method described above. The surface layer was determined to be crystalline when peaks derived from a crystalline structure were observed in the obtained X-ray diffraction pattern. From this result and the composition of the solution to be attached to the base material described above, it was determined that the surface layer of the obtained active material particles was crystalline, and its composition formula was LiNbO 2.9 Br 0.2 It is thought that this is the case.

[0147] (Fabrication of all-solid-state secondary batteries) Using the obtained active material particles, an all-solid-state secondary battery of Example 11 was fabricated in the following manner. In a glove box with an argon atmosphere, the above active material particles, a sulfide solid electrolyte (Li6PS5Cl), and a conductive agent (acetylene black) were mixed in an agate mortar. Next, a binder (SBR) and butyl butyrate as a solvent were added to this mixture, and the mixture was kneaded in a hybrid mixer to form a positive electrode mixture. The resulting positive electrode mixture was applied to aluminum foil (average thickness 20 μm) as the positive electrode substrate, and after drying the solvent using a YBA-type baker applicator, the positive electrode active material layer had a basis weight of 15 mg cm. -2 More than 25mg cm -2 The coating was performed as follows. This was dried in a dryer in an argon atmosphere set at a temperature at which the solvent volatilized, forming a positive electrode active material layer on the positive electrode substrate. This was then punched out into a circle with a diameter of 10 mm to prepare a positive electrode for evaluation. Next, 80 mg of sulfide solid electrolyte (Li6PS5Cl) was inserted into a ceramic powder compactor with an inner diameter of 10 mm and pressure-molded using a uniaxial press at a pressure of 100 MPa for several seconds to form an isolation layer. After releasing the pressure, the prepared positive electrode was placed on one side of the isolation layer and pressure-molded using a uniaxial press at 360 MPa for 5 minutes. After releasing the pressure, indium foil (average thickness 300 μm, diameter 8 mm, manufactured by Nilaco) and lithium foil (average thickness 300 μm, diameter 6 mm, manufactured by Honjo Metal Co., Ltd.) as negative electrodes, and SUS316L foil (manufactured by Nilaco) as negative electrode substrates were placed on the side opposite the bonding surface of the positive electrode and bonded using a uniaxial press at a pressure of 50 MPa for several seconds. The battery of Example 11 was obtained by removing it from the ceramic powder compactor.

[0148] [Example 12] The lithium bromide in the solution applied to the base material was changed to lithium iodide, and the composition of the surface layer was changed to LiNbO 2.9 I 0.2 The active material particles and all-solid-state secondary battery of Example 12 were produced in the same manner as in Example 11, except that the surface layer of the obtained active material particles was confirmed to be crystalline by the same method as in Example 11.

[0149] Comparative Example 2 Active material particles and an all-solid-state secondary battery of Comparative Example 2 were produced in the same manner as in Example 11, except that lithium bromide was not used in the solution to be attached to the base material and the composition of the surface layer was LiNbO. The surface layer of the obtained active material particles was confirmed to be amorphous by the same method as in Example 11.

[0150] Comparative Example 3 The lithium bromide in the solution applied to the base material was changed to lithium chloride, and the composition of the surface layer was changed to LiNbO 2.9 Cl 0.2 Active material particles and an all-solid-state secondary battery of Comparative Example 3 were produced in the same manner as in Example 11, except that the surface layer of the obtained active material particles was confirmed to be amorphous by the same method as in Example 11.

[0151] [Reference Example 1] The active material particles and all-solid-state secondary battery of Reference Example 1 were produced in the same manner as in Example 11, except that the formation of the surface layer was not performed on the base material.

[0152] [Evaluation 2] <Capacity Confirmation Test 2> For each of the obtained all-solid-state secondary batteries, a Capacity Confirmation Test 2 was performed at 50°C as follows. Constant current and constant voltage charging was performed with a charging current of 0.1C and a charging cut-off voltage of 3.75V. The end condition of charging was until the charging current reached 0.025C. Thereafter, a rest period of 10 minutes was provided. Thereafter, constant current discharging was performed with a discharging current of 0.1C and a discharging cut-off voltage of 2.25V. The percentage of the discharge capacity with respect to the charging capacity in the first charge-discharge cycle was determined and defined as the first charge-discharge efficiency. The results are shown in Table 2.

[0153] [Table 2]

[0154] From Table 2, it can be seen that according to the positive electrode active material of the example provided with a crystalline surface layer containing each element of lithium, niobium, oxygen, and halogen on the surface of the base material composed of a material capable of occluding and releasing lithium ions, when the ratio of the total molar number of the halogen to the molar number of the niobium is c, and 0 < c ≤ 1.0 is satisfied, an all-solid-state secondary battery with a higher first charge-discharge efficiency can be obtained than the positive electrode active materials of the comparative example provided with an amorphous surface layer and the reference example not provided with a surface layer. Also, from the results of Comparative Example 2, Comparative Example 3, and Reference Example 1, it can be seen that when the positive electrode active material is provided with an amorphous surface layer containing halogen, the first charge-discharge efficiency is lower than when the surface layer does not contain halogen and when the surface layer is not provided. From the above results, it can be said that the effect of increasing the first charge-discharge efficiency by the surface layer containing each element of lithium, niobium, oxygen, and halogen is peculiar to the case where the surface layer is crystalline. [Industrial Applicability]

[0155] The present invention is applicable to power storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, etc., and electrodes provided therefor. [Explanation of symbols]

[0156] 1 positive electrode 2 negative electrode 3 isolation layer 4. Positive electrode substrate 5 Cathode active material layer 6 Negative electrode active material layer 7. Negative electrode substrate 10 Energy storage element (all-solid-state secondary battery) 20 Energy storage unit 30 Electricity storage device

Claims

1. an active material base material and a coating layer that coats at least a portion of the surface of the active material base material; the coating layer contains niobium atoms and phosphorus atoms, The active material particles have a phosphorus atom content of more than 0 mol % and not more than 80 mol % relative to the total content of the niobium atoms and the phosphorus atoms in the coating layer.

2. 2. The active material particles according to claim 1, wherein the coating layer contains a composite oxide containing the niobium atoms and the phosphorus atoms.

3. 3. The active material particles according to claim 2, wherein the composite oxide is represented by the following formula 1: Li ｘ Nb （１－ｙ） P ｙ O ｚ A ｗ ・・・1 In Formula 1, A is one or more elements other than Li, Nb, P, and O. x is a number greater than 0 and equal to or less than 2. y is a number greater than 0 and equal to or less than 0.

8. z is a number greater than 2 and equal to or less than 4. w is a number greater than 0 and equal to or less than 1.

4. 4. The active material particles according to claim 1, wherein the content of the coating layer relative to the content of the active material base is 0.01% by mass or more and 2.0% by mass or less.

5. A base material composed of a material capable of absorbing and releasing lithium ions; and present on the surface of the base material, containing the elements lithium, niobium, oxygen, and halogens; When the ratio of the total number of moles of the halogen to the number of moles of the niobium is c, 0<c≦1.0 is satisfied; and It is crystalline surface layer A positive electrode active material for an all-solid-state secondary battery comprising:

6. The positive electrode active material for an all solid state secondary battery according to claim 5 , wherein the halogen is at least one selected from bromine and iodine.

7. The surface layer has the composition formula Li ａ NbO ｂ X ｃ (wherein X is a halogen, and a, b, and c are real numbers satisfying 0.5≦a≦1.5, 2.5≦b≦3.5, and 0<c≦1.0).

8. An electrode comprising the active material particles according to any one of claims 1 to 4 or the positive electrode active material for an all-solid-state secondary battery according to any one of claims 5 to 7.

9. An energy storage element comprising the electrode according to claim 8 .

10. An all-solid-state secondary battery comprising the electrode according to claim 8.

11. Coating at least a portion of the surface of a particulate active material base material with a coating agent containing niobium atoms and phosphorus atoms; heat-treating the active material base material coated with the coating agent; In this order, The method for producing active material particles, wherein the content of the phosphorus atoms in the coating agent is more than 0 mol % and 80 mol % or less relative to the total content of the niobium atoms and the phosphorus atoms.

12. An electricity storage device comprising two or more electricity storage elements, and at least one of the electricity storage element according to claim 9 or the all-solid-state secondary battery according to claim 10.

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