Positive electrode active material for power storage device, positive electrode, and power storage device

Abstract

To provide: a positive electrode active material and a positive electrode that can increase the discharge capacity of a storage device during high-rate discharge and the discharge capacity retention rate after charge-discharge cycling; and a storage device that has a large discharge capacity during high-rate discharge and a large discharge capacity retention rate after charge-discharge cycling.SOLUTION: A positive electrode active material for a power storage device according to an embodiment of the present invention includes active material particles containing a lithium transition metal composite oxide and a coating layer that coats at least a portion of the active material particles, and the coating layer consists substantially of a compound containing lithium, aluminum, silicon, and oxygen.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for an energy storage device, a positive electrode, and an energy storage device. [Background technology]

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as automobiles. Non-aqueous electrolyte 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 charge-transporting ions between the electrodes. As non-aqueous electrolyte secondary batteries, all-solid-state batteries have been proposed that use a sulfide solid electrolyte or the like as the non-aqueous electrolyte instead of a liquid electrolyte containing an organic solvent or the like. Furthermore, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] Lithium transition metal composite oxides are sometimes used as the positive electrode active material of electricity storage elements (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-170190 Summary of the Invention [Problem to be solved by the invention]

[0005] When a lithium transition metal composite oxide is used as a positive electrode active material, a side reaction may occur between the positive electrode active material and the electrolyte, which may result in a decrease in the discharge capacity of the energy storage device during high-rate discharge or with repeated charge-discharge cycles.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a positive electrode active material and a positive electrode that can increase the discharge capacity of a storage element during high-rate discharge and the discharge capacity retention rate after charge-discharge cycling, and an energy storage element that has a large discharge capacity during high-rate discharge and a large discharge capacity retention rate after charge-discharge cycling. [Means for solving the problem]

[0007] A positive electrode active material for a storage element according to one embodiment of the present invention comprises active material particles containing a lithium transition metal composite oxide and a coating layer that coats at least a portion of the active material particles, and the coating layer consists essentially of a compound containing lithium, aluminum, silicon, and oxygen.

[0008] A positive electrode according to another embodiment of the present invention includes the positive electrode active material for an energy storage device according to the embodiment of the present invention and a sulfide solid electrolyte.

[0009] An energy storage device according to another aspect of the present invention includes the positive electrode according to the aspect of the present invention. [Effects of the Invention]

[0010] The positive electrode active material for an energy storage device and the positive electrode according to one embodiment of the present invention can increase the discharge capacity of the energy storage device during high-rate discharge and the discharge capacity retention rate after charge-discharge cycling. Furthermore, the energy storage device according to one embodiment of the present invention has a large discharge capacity during high-rate discharge and a large discharge capacity retention rate after charge-discharge cycling. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery, which is one embodiment of the energy storage element of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device configured by assembling a plurality of electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, an outline of the positive electrode active material for an energy storage device, the positive electrode, and the energy storage device disclosed in this specification will be described.

[0013] [1] A positive electrode active material for a storage device according to one embodiment of the present invention comprises active material particles containing a lithium transition metal composite oxide and a coating layer that coats at least a portion of the active material particles, and the coating layer consists essentially of a compound containing lithium, aluminum, silicon, and oxygen.

[0014] The positive electrode active material for an energy storage device described in [1] above can increase the discharge capacity of an energy storage device during high-rate discharge and the discharge capacity retention rate after charge-discharge cycling. While the reason for this is unclear, the following is presumed. When active material particles containing a lithium transition metal composite oxide are used as the positive electrode active material, side reactions can occur between the active material particles and the electrolyte. Therefore, when a positive electrode containing such active material particles is used, the discharge capacity of an energy storage device during high-rate discharge and the discharge capacity retention rate after charge-discharge cycling may be reduced. In contrast, the positive electrode active material for an energy storage device described in [1] above has a coating layer that covers at least a portion of the active material particles containing a lithium transition metal composite oxide, thereby suppressing side reactions between the active material particles and the electrolyte. Furthermore, the coating layer is composed essentially of a compound containing lithium, aluminum, silicon, and oxygen. Because this compound contains both aluminum and silicon, it has superior oxidation resistance compared to compounds containing each element alone. Furthermore, because the compound contains lithium, it can suppress depletion of lithium ions that function as charge-transport ions during charge-discharge cycling. Furthermore, according to the findings of the inventors, if the coating layer contains impurities such as conductive materials, there is a possibility that side reactions between the active material particles and the electrolyte may not be sufficiently suppressed. However, in the positive electrode active material for a storage device described in [1] above, the coating layer is composed essentially of compounds containing lithium, aluminum, silicon, and oxygen, so that the effect of suppressing side reactions between the active material particles and the electrolyte is easily achieved. For these reasons, it is presumed that the positive electrode active material for a storage device described in [1] above can increase the discharge capacity during high-rate discharge of the storage device and the discharge capacity retention rate after charge-discharge cycling.

[0015] [2] In the positive electrode active material for a storage device according to the above [1], the molar ratio of lithium element to the total of aluminum element and silicon element, as determined by X-ray photoelectron spectroscopy, may be 1.0 or more, the molar ratio of aluminum element to all transition metal elements in the lithium transition metal composite oxide may be 0.1 or more, and the molar ratio of silicon element to the transition metal elements may be 0.1 or more.

[0016] In the positive electrode active material for an energy storage device described in [2] above, the molar ratio of the lithium element obtained by X-ray photoelectron spectroscopy is equal to or greater than the lower limit, thereby sufficiently suppressing depletion of lithium ions that function as charge-transport ions during charge-discharge cycling. Furthermore, the molar ratios of the aluminum element and the silicon element obtained by X-ray photoelectron spectroscopy are each equal to or greater than the lower limit, so that sufficient amounts of the aluminum element and the silicon element originating from the coating layer are present on the surface of the positive electrode active material for an energy storage device. This sufficiently enhances the oxidation resistance of the coating layer, thereby further increasing the discharge capacity during high-rate discharge of the energy storage device and the discharge capacity retention rate after charge-discharge cycling.

[0017] When the positive electrode active material for an energy storage device is contained in an energy storage device, a measurement sample used for X-ray photoelectron spectroscopy (XPS) analysis is prepared by the following method. First, the energy storage element is discharged at a constant current of 0.05 C to the minimum voltage limit for normal use. Next, the energy storage element is disassembled to remove the electrode body. The electrode body is observed, and if it is confirmed that the removed electrode body contains a solid electrolyte, the electrode body is immersed in a solvent that dissolves only the solid electrolyte, such as ethanol or ion-exchanged water, to remove the solid electrolyte. Next, the surface of the positive electrode is observed, and if it is confirmed that the positive electrode active material layer contains a particulate positive electrode active material, the positive electrode is immersed in a solvent that dissolves only the binder, such as butyl butyrate, to remove the positive electrode substrate and the binder from the positive electrode active material layer, 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. On the other hand, if it is confirmed that the surface of the positive electrode contains a film-like positive electrode active material, the positive electrode is used as a measurement sample either as is or cut to an appropriate size. In this case, the surface of the measurement sample to be subjected to XPS analysis is the surface on which the positive electrode active material layer is formed.

[0018] The XPS analysis was performed using an AXIS NOVA (KRATOS ANALYTICAL) with a monochromated AlKα X-ray source and a pass energy of 20 eV. The molar ratio of each element was calculated by analyzing the spectra obtained using CasaXPS (Casa Software). First, the peak attributable to sp2 carbon in C1s was set to 284.5 eV, and all spectra were corrected. Note that the peak attributable to sp2 carbon is a peak derived from carbon elements contained in impurities attached to the surface of the measurement sample. Next, the background of each spectrum was removed using the Shirley method. The areas of the peaks attributable to each element (Li1s, Al2p, Si2p, Ni3p, Co3p, Mn3p, etc.) were calculated, and the corrected peak areas of each element were calculated by correcting these values using the relative sensitivity coefficients corresponding to each element. The molar ratio of each element was calculated as the ratio of these corrected peak areas.

[0019] [3] A positive electrode according to another aspect of the present invention includes the positive electrode active material for an energy storage device according to [1] or [2] above and a sulfide solid electrolyte.

[0020] The positive electrode described in [3] above contains the positive electrode active material for a storage device described in [1] or [2] above, and therefore can increase the discharge capacity of the storage device during high-rate discharge and the discharge capacity retention rate after charge-discharge cycling. Furthermore, sulfide solid electrolytes are particularly susceptible to side reactions with lithium transition metal composite oxides. Therefore, the advantage of the present invention, namely, suppression of side reactions between the active material particles and the electrolyte, can be particularly pronounced.

[0021] [4] An energy storage device according to another aspect of the present invention includes the positive electrode described in [3] above.

[0022] The energy storage element described in [4] above includes the positive electrode described in [3] above, and therefore has a large discharge capacity during high-rate discharge and a large discharge capacity retention rate after charge-discharge cycles.

[0023] [5] The energy storage element according to [4] above may be an all-solid-state battery.

[0024] The energy storage element described in [5] above is an all-solid-state battery, and therefore the advantages of the present invention, such as a large discharge capacity during high-rate discharge and a large discharge capacity retention rate after charge-discharge cycling, can be particularly significantly obtained.

[0025] Hereinafter, a positive electrode active material for an energy storage device, a method for manufacturing a positive electrode active material for an energy storage device, a positive electrode, an energy storage device, a method for manufacturing 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.

[0026] [Positive electrode active material for energy storage devices] A positive electrode active material for a storage element according to one embodiment of the present invention (hereinafter also simply referred to as "positive electrode active material") has active material particles containing a lithium transition metal composite oxide and a coating layer that coats at least a portion of the active material particles.

[0027] (active material particles) The active material particles contain a lithium transition metal composite oxide.

[0028] The lithium transition metal composite oxide preferably contains at least one of nickel, cobalt, and manganese, more preferably nickel, cobalt, and manganese, and even more preferably a lithium nickel-cobalt-manganese composite oxide. The active material particles can contain one or more lithium transition metal composite oxides.

[0029] The lithium transition metal composite oxide may further contain transition metal elements other than nickel, manganese, and cobalt, and typical metal elements other than lithium, such as aluminum. However, the lower limit of the molar ratio ((Ni + Mn + Co) / Me) of the total of nickel, manganese, and cobalt to all metal elements (Me) excluding lithium in the lithium transition metal composite oxide is preferably 0.9, more preferably 0.95, and even more preferably 0.99. When the metal elements other than lithium in the lithium transition metal composite oxide are essentially composed of only two elements, nickel and manganese, or three elements, nickel, manganese, and cobalt, effects such as a large discharge capacity during high-rate discharge and a large discharge capacity retention rate after charge-discharge cycling are particularly sufficiently exhibited.

[0030] The molar ratio (Ni / Me) of nickel element to all metal elements (Me) excluding lithium element in the lithium transition metal composite oxide is preferably 0.10 or more and 0.90 or less, more preferably 0.20 or more and 0.70 or less, and even more preferably 0.30 or more and 0.60 or less.

[0031] The molar ratio (Mn / Me) of manganese element to all metal elements (Me) excluding lithium element in the lithium transition metal composite oxide is preferably 0.05 or more and 0.60 or less, more preferably 0.10 or more and 0.55 or less, and even more preferably 0.20 or more and 0.50 or less.

[0032] The molar ratio (Co / Me) of cobalt element to all metal elements (Me) excluding lithium element in the lithium transition metal composite oxide is preferably 0 or more and less than 0.50, more preferably 0.10 or more and 0.45 or less, and even more preferably 0.20 or more and 0.40 or less.

[0033] The lithium transition metal composite oxide is preferably a lithium transition metal composite oxide having a layered α-NaFeO2 type crystal structure. The lithium transition metal composite oxide is preferably a compound represented by the following formula (1):

[0034] Li 1+α Me 1-α O2···(1) In formula (1), Me is a metal element other than Li. 0≦α<1. In formula (1), α may be 0 or more and 0.5 or less, 0 or more and 0.3 or less, or 0 or more and 0.1 or less. The preferred elemental composition and molar ratio of Me in formula (1) are the same as the preferred elemental composition and molar ratio of each element relative to all metal elements (Me) other than lithium in the lithium transition metal composite oxide described above.

[0035] The active material particles may further contain a positive electrode active material other than the lithium transition metal composite oxide. As the other positive electrode active material, various conventionally known positive electrode active materials can be used. However, the content of the lithium transition metal composite oxide in the active material particles is preferably 90% by mass or more, more preferably 99% by mass or more. By using the lithium transition metal composite oxide as the active material particles, the effects of the present invention can be particularly fully exhibited.

[0036] The average particle size of the active material particles is preferably, for example, 0.1 μm to 20 μm, more preferably 0.5 μm to 12 μm, even more preferably 1 μm to 8 μm, and even more preferably 2 μm to 5 μm. Setting the average particle size of the active material particles above the lower limit facilitates the production and handling of the active material particles. Setting the average particle size of the active material particles below the upper limit improves the electronic conductivity of the positive electrode containing the active material particles and increases the reaction area, thereby improving output performance. The term "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 a diluted solution of particles diluted with a solvent in accordance with JIS-Z-8825 (2013).

[0037] To obtain powders such as active material particles 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.

[0038] (covering layer) The coating layer may cover the entire active material particles or may cover only a portion of them. The coating layer is composed essentially of a compound containing lithium, aluminum, silicon, and oxygen (hereinafter also referred to as "coating compound"). The coating layer being "substantially" composed of the coating compound means that the content of the coating compound in the coating layer is 99% by mass or more, and the content of the coating compound in the coating layer may be 99.5% by mass or more, 99.8% by mass or more, or even 100% by mass.

[0039] The content of the conductive material in the coating layer is preferably 1% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and even more preferably 0.0% by mass. By keeping the content of the conductive material in the coating layer below the upper limit, it becomes easier to suppress side reactions between the active material particles and the electrolyte. Here, the conductive material is a material that has conductivity. Whether or not a material has "conductivity" is determined by whether or not the material has a volume resistivity of 10 or less as measured in accordance with JIS-H-0505 (1975). -2 The judgment is made using Ω·cm as a threshold value. Examples of conductive materials include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include non-graphitic carbon and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber and pitch-based carbon fiber. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. The conductive agent may be in the form of powder or fiber.

[0040] The lower limit of the molar ratio (Li / (Al+Si)) of lithium (Li) to the sum of aluminum (Al) and silicon (Si) in the coating layer is preferably 0.3, more preferably 0.5. The lower limit of the molar ratio may be 0.8, 1.0, or 1.2. When the molar ratio is equal to or greater than the lower limit, depletion of lithium ions that function as charge-transport ions during charge-discharge cycles can be sufficiently suppressed. This allows the energy storage device to have a higher discharge capacity during high-rate discharge and a higher discharge capacity retention rate after charge-discharge cycles. On the other hand, the upper limit of the molar ratio (Li / (Al+Si)) is preferably 10.0, more preferably 5.0, and even more preferably 2.0, from the viewpoint of keeping the aluminum and silicon contents within appropriate ranges.

[0041] The lower limit of the content of the coating layer based on the mass of the active material particles is preferably 0.50 mass%, more preferably 0.60 mass%, even more preferably 0.70 mass%, and even more preferably 0.80 mass%, from the viewpoint of suppressing side reactions between the active material particles and the electrolyte, while the upper limit of the content of the coating layer is preferably 2.00 mass%, more preferably 1.50 mass%, even more preferably 1.20 mass%, and even more preferably 1.00 mass%, from the viewpoint of ensuring the output performance of an energy storage device using the positive electrode active material.

[0042] The lower limit of the ionic conductivity of the coating layer is 1×10 from the viewpoint of maintaining the discharge capacity of the positive electrode active material. -12 S / cm is preferred, 1×10 -11 S / cm is more preferable, and 5×10 -11 On the other hand, the upper limit of the ionic conductivity of the coating layer is 1×10 -7 S / cm, and 1×10 -8 S / cm, and 1×10 -9 S / cm, and 1×10 -10 S / cm may also be used. The ionic conductivity is determined by measuring AC impedance using the following method. In an argon atmosphere with a dew point of -50°C or lower, 120 mg of the coating layer sample powder is placed in a powder molder with an inner diameter of 10 mm and then uniaxially pressed using a hydraulic press at 50 MPa or lower. After releasing the pressure, 120 mg of SUS316L powder is placed on the top surface of the sample as a current collector and then uniaxially pressed using a hydraulic press again at 50 MPa or lower. Next, 120 mg of SUS316L powder is placed on the bottom surface of the sample as a current collector and then uniaxially pressed at 400 MPa for 5 minutes to obtain a pellet for ionic conductivity measurement. This pellet for ionic conductivity measurement is inserted into a Hohsen HS cell, and AC impedance measurement is performed at a specified temperature. The measurement conditions are an applied voltage amplitude of 20 mV, a frequency range of 1 MHz to 100 mHz, and a measurement temperature of 50°C.

[0043] The lower limit of the molar ratio (Li / (Al+Si)) of lithium (Li) to the sum of aluminum (Al) and silicon (Si), obtained by X-ray photoelectron spectroscopy of the positive electrode active material, is preferably 1.0, more preferably 2.0, even more preferably 2.5, and may even be 3.0. When the molar ratio is equal to or greater than the lower limit, the discharge capacity of the energy storage device during high-rate discharge and the discharge capacity retention rate after charge / discharge cycling can be increased. On the other hand, the upper limit of the molar ratio (Li / (Al+Si)) is preferably 10.0, more preferably 7.0, even more preferably 6.0, and even more preferably 5.5, from the viewpoint of keeping the contents of aluminum and silicon within appropriate ranges.

[0044] The lower limit of the molar ratio (Al / Mt) of aluminum (Al) to all transition metal elements (Mt) in the lithium transition metal composite oxide, as determined by X-ray photoelectron spectroscopy of the positive electrode active material, is preferably 0.1, more preferably 0.5, and may be 1.0 or 1.5. When the molar ratio (Al / Mt) is equal to or greater than the lower limit, a sufficient amount of aluminum element originating from the coating layer is present on the surface of the positive electrode active material for a storage battery element, thereby sufficiently enhancing the oxidation resistance of the coating layer. On the other hand, the upper limit of the molar ratio (Al / Mt) is preferably 4.0, more preferably 3.5, even more preferably 3.0, even more preferably 2.8, and may be 2.5, from the viewpoint of keeping the aluminum element content within an appropriate range.

[0045] The lower limit of the molar ratio (Si / Mt) of silicon (Si) to all transition metal elements (Mt) in the lithium transition metal composite oxide, as determined by X-ray photoelectron spectroscopy of the positive electrode active material, is preferably 0.1, more preferably 0.3, even more preferably 0.5, and even more preferably 0.8. When the molar ratio (Si / Mt) is equal to or greater than the lower limit, a sufficient amount of silicon originating from the coating layer is present on the surface of the positive electrode active material for a storage battery element, thereby sufficiently enhancing the oxidation resistance of the coating layer. On the other hand, the upper limit of the molar ratio (Si / Mt) is preferably 3.0, more preferably 2.5, even more preferably 2.0, and even more preferably 1.5, from the viewpoint of keeping the silicon content within an appropriate range.

[0046] The lower limit of the molar ratio ((Al+Si) / Mt) of the sum of aluminum (Al) and silicon (Si) to all transition metal elements (Mt) in the lithium transition metal composite oxide, obtained by X-ray photoelectron spectroscopy analysis of the positive electrode active material, is preferably 1.0, more preferably 1.5, and even more preferably 2.0. When the molar ratio ((Al+Si) / Mt) is equal to or greater than the lower limit, sufficient amounts of aluminum and silicon originating from the coating layer are present on the surface of the positive electrode active material for a storage battery element, thereby sufficiently enhancing the oxidation resistance of the coating layer. On the other hand, the upper limit of the molar ratio ((Al+Si) / Mt) is preferably 5.0, more preferably 4.0, and in some cases even more preferably 3.0, from the viewpoint of keeping the contents of aluminum and silicon within appropriate ranges.

[0047] The positive electrode active material may be in a particulate form. The average particle size of the positive electrode active material is, for example, preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 12 μm, even more preferably 1 μm to 8 μm, and even more preferably 2 μm to 5 μm. By setting the average particle size of the positive electrode active material to the above lower limit or above, the production and handling of the positive electrode active material becomes easier. By setting the average particle size of the positive electrode active material to the above upper limit or below, the electronic conductivity of the positive electrode containing the positive electrode active material is improved, and the reaction area is increased, resulting in improved output performance, etc. The average particle size of the positive electrode active material can be adjusted by, for example, adjusting the average particle size of the active material particles.

[0048] The positive electrode active material may further contain components other than the active material particles and the coating layer. However, the total content of the active material particles and the coating layer in the positive electrode active material is preferably 90% by mass or more, more preferably 99% by mass or more, and may even be 100% by mass. In this way, when the positive electrode active material is mainly composed of the active material particles and the coating layer, the effects of the present invention can be particularly fully exhibited.

[0049] [Method of manufacturing a positive electrode active material for an energy storage device] A method for producing a positive electrode active material (positive electrode active material for a storage device) of this embodiment includes, for example, preparing active material particles containing a lithium transition metal composite oxide, supplying a precursor of a compound containing lithium, aluminum, silicon, and oxygen to the surfaces of the active material particles, and heating the active material particles and the precursor. In addition to the above, the method for producing a positive electrode active material for a storage device may also include pulverizing the active material particles, stirring the active material particles and the precursor, etc.

[0050] In the supplying step, the precursor may be a mixture of multiple compounds, such as a mixture of a compound containing lithium, a compound containing aluminum, a compound containing silicon, and a compound containing oxygen. Alternatively, the precursor may be a mixture of an organic salt of lithium, an organic salt of aluminum, an organic compound containing silicon, etc. In the supplying step, the precursor may be dissolved in an organic solvent and sprayed onto the active material particles. The precursor may be selected so that, after heating, substantially only compounds containing lithium, aluminum, silicon, and oxygen remain on the surfaces of the active material particles.

[0051] A known coating device may be used in the supplying and heating. From the viewpoint of forming a uniform coating layer on the surfaces of the active material particles, for example, a tumbling fluidized bed coating device can be used as the coating device.

[0052] [Positive electrode] A positive electrode according to one embodiment of the present invention includes a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer. The positive electrode active material layer contains the positive electrode active material according to one embodiment of the present invention. The positive electrode may be a positive electrode for an energy storage device or a positive electrode for an all-solid-state battery.

[0053] The positive electrode substrate is conductive. Examples of the material for the positive electrode substrate include metals such as aluminum, titanium, tantalum, and stainless steel, as well as alloys thereof. Among these, aluminum or aluminum alloys are preferred in terms of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred in terms of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0054] 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 element.

[0055] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0056] As described above, the positive electrode active material layer includes the positive electrode active material according to one embodiment of the present invention. The positive electrode active material layer preferably includes a sulfide solid electrolyte. A side reaction is particularly likely to occur between the sulfide solid electrolyte and the positive electrode active material containing a lithium transition metal composite oxide. Therefore, the advantage of the present invention, namely, suppressing a side reaction between the active material particles of the positive electrode active material and the electrolyte, is particularly pronounced. The sulfide solid electrolyte may coat at least a portion of the positive electrode active material. The sulfide solid electrolyte may also form a mixture with the positive electrode active material. The positive electrode active material layer further includes optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary. The positive electrode active material layer is formed from a positive electrode mixture containing the positive electrode active material and other optional components.

[0057] The positive electrode active material layer may contain a positive electrode active material other than the positive electrode active material according to one embodiment of the present invention, provided that the content of the positive electrode active material in the total positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0058] The sulfide solid electrolyte preferably has high lithium ion conductivity, and examples thereof 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 P, Si, Ge, B, Al, Ga, or In.) Li6PS5Cl, Li 10 GeP2S 12 As the sulfide solid electrolyte, an argyrodite-type solid electrolyte such as Li6PS5Cl can be suitably used.

[0059] The positive electrode active material layer may contain other common solid electrolytes in addition to the sulfide solid electrolyte. Examples of such solid electrolytes include oxide-based solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes. The positive electrode active material layer may also contain a plurality of different solid electrolytes in addition to the sulfide solid electrolyte. However, the content of the sulfide solid electrolyte in the total solid electrolyte in the positive electrode active material layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0060] The total content of the positive electrode active material in the positive electrode active material layer is preferably 60% by mass to 95% by mass, more preferably 70% by mass to 90% by mass. By setting the total content of the positive electrode active material within this range, it is possible to increase the discharge capacity and the energy density.

[0061] 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 viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0062] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 15% by mass. By setting the content of the conductive agent within this range, the energy density of the energy storage element can be increased.

[0063] 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.

[0064] The content of the binder in the positive electrode 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 positive electrode active material and the like can be stably maintained.

[0065] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The content of the thickener in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a thickener.

[0066] The filler is not particularly limited. Examples of fillers 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; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; and artificial products thereof. The content of the filler in the positive electrode active material layer is preferably, for example, 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a filler.

[0067] The positive electrode 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 positive electrode active material, solid electrolyte such as a sulfide solid electrolyte, conductive agent, binder, thickener, and filler.

[0068] [Energy storage element] An energy storage element according to one embodiment of the present invention will be described using an all-solid-state battery as a specific example. The energy storage element 10 shown in FIG. 1 is an all-solid-state battery, and is a secondary battery in which a positive electrode 1 and a negative electrode 2 according to one embodiment of the present invention are arranged with an isolation layer 3 between them. In the energy storage element of this embodiment, the positive electrode 1 has 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 has 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. In the energy storage element 10 shown in FIG. 1, the negative electrode active material layer 6, the isolation layer 3, the positive electrode 1, and the positive electrode substrate 4 are stacked in this order on the negative electrode substrate 7.

[0069] <Positive electrode> The positive electrode 1 has a positive electrode substrate 4 and a positive electrode active material layer 5 disposed on the positive electrode substrate 4 directly or via an intermediate layer. The positive electrode substrate 4, the intermediate layer, and the positive electrode active material layer 5 may be the same as the positive electrode substrate, the intermediate layer, and the positive electrode active material layer of the positive electrode according to one embodiment of the present invention described above.

[0070] <Negative electrode> The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6 disposed on the negative electrode substrate 7 directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above. Hereinafter, the negative electrode 2 will be simply referred to as the "negative electrode," the negative electrode substrate 7 will be simply referred to as the "negative electrode substrate," and the negative electrode active material layer 6 will be simply referred to as the "negative electrode active material layer."

[0071] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, carbon materials, and the like are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0072] 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.

[0073] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a solid electrolyte, a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the solid electrolyte, the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0074] The negative electrode 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, Ta, Hf, Nb, and W as components other than the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0075] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. 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 of the material 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). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0076] "Graphite" refers to graphite that has an average lattice spacing (d002 ) 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.

[0077] "Non-graphitic carbon" refers to the 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.

[0078] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode is 0.7 V or higher.

[0079] "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.

[0080] "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.

[0081] 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 produced 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 electronic conductivity of the negative electrode active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder with a predetermined particle size. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material layer may be in the form of a foil.

[0082] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0083] The negative electrode active material layer may contain a solid electrolyte. When the negative electrode active material layer contains a solid electrolyte, the content of the solid electrolyte is preferably 1% by mass or more and 40% by mass or less, and more preferably 2% by mass or more and 10% by mass or less. By setting the content of the solid electrolyte within the above range, the electric capacity of the all-solid-state battery 10 can be increased.

[0084] When the negative electrode active material layer contains a solid electrolyte, it may be a mixture of the above-mentioned negative electrode active material and the solid electrolyte.

[0085] <Isolation layer> The separator 3 contains a solid electrolyte. The solid electrolyte contained in the separator 3 is preferably the sulfide solid electrolyte described above. In addition to the sulfide solid electrolyte, other general solid electrolytes may also be contained as the solid electrolyte. The content of the solid electrolyte in the separator 3 is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and even more preferably substantially 100% by mass.

[0086] The separator 3 may contain optional components such as a binder, a thickener, a filler, etc. The optional components such as a binder, a thickener, a filler, etc. can be selected from the materials exemplified for the positive electrode.

[0087] When the energy storage device 10 is an all-solid-state battery, both the positive electrode active material layer 5 and the separator 3 contain a solid electrolyte. When the negative electrode active material is in the form of particles, the negative electrode active material layer 6 also contains a solid electrolyte. When the negative electrode active material layer 6 is in the form of a foil, the negative electrode active material layer 6 does not need to contain a solid electrolyte. As the solid electrolyte, all layers in the energy storage device 10 may contain a sulfide solid electrolyte, all layers may contain the same solid electrolyte as the positive electrode active material layer 5, one layer may contain multiple different types of solid electrolytes, or each layer may contain a different solid electrolyte.

[0088] [Electricity storage device] The energy storage element of this embodiment can be mounted as an energy storage device configured by assembling a plurality of energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or 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 included in the energy storage device. 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 two or more energy storage elements 10, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage units 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements 10.

[0089] [Method of manufacturing an energy storage element] The method for producing the energy storage device of this embodiment can be appropriately selected from known methods, except for using the method for producing the positive electrode active material for the energy storage device described above as a method for producing the positive electrode active material in the positive electrode. The production method includes, for example, preparing a positive electrode, preparing a separator, preparing a negative electrode, and stacking the positive electrode, separator, and negative electrode.

[0090] [Other embodiments] The positive electrode active material for an energy storage device, the positive electrode, and the energy storage device of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit and scope of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, a part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment. For example, the energy storage device of the present invention may include layers other than the positive electrode, separator, and negative electrode, such as an adhesive layer. The present invention can also be applied to an energy storage device including a bipolar electrode. The energy storage device of the present invention may be an all-solid-state battery, a capacitor, or the like. [Example]

[0091] [Example 1] The active material particles have an α-NaFeO2 type crystal structure and LiNi 0.5 Co 0.2 Mn 0.3Particles of lithium transition metal composite oxide represented by the formula O2 were used. A coating process was performed by spraying a coating solution containing ethoxylithium, aluminum isopropoxide, tetraethoxysilane, and ethanol while fluidizing the active material particles with air heated to 100°C. The coating process was performed using a tumbling fluidized coating device (Powrex Corporation's "FD-MD-micro"). The active material particles were then heated at 400°C in an air atmosphere to obtain a positive electrode active material coated with a coating layer consisting essentially of a compound containing lithium, aluminum, silicon, and oxygen. The molar ratio of lithium, aluminum, and silicon in the coating solution was 1:1:1. The content of the coating layer in the resulting positive electrode active material was 0.86% by mass based on the mass of the active material particles. The coating solution was dried separately and then heated at 400°C in an air atmosphere to obtain a sample. The ionic conductivity of the coating layer was measured. The ionic conductivity of the coating layer was 1×10 at 50°C. -10 It was below S / cm.

[0092] [Examples 2 to 5 and Comparative Examples 1 and 2] The positive electrode active materials of Examples 2 to 5 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the molar ratio of lithium element, aluminum element, and silicon element in the coating solution and the content of the coating layer based on the mass of the active material particles were set as shown in Table 1. In Table 1, a molar ratio value of 0 means that the corresponding element is not contained.

[0093] Each positive electrode active material was subjected to XPS analysis according to the procedure described above. The molar ratios of each element obtained by XPS analysis are shown in Table 1. In Table 1, "-" means that the value is less than 0.1.

[0094] [Preparation of positive electrode] Positive electrodes were fabricated using the positive electrode active materials of the above-mentioned Examples and Comparative Examples. The positive electrode active material, an argyrodite-type sulfide solid electrolyte represented by Li6PS5Cl, and fibrous carbon as a conductive agent were weighed out in a predetermined mass ratio. Next, SBR as a binder and butyl butyrate as a solvent were mixed with this mixture to a solid content ratio of 60 mass%, and the mixture was kneaded in a hybrid mixer to form a positive electrode mixture. The obtained positive electrode mixture was applied to an aluminum foil (average thickness 20 μm) as a positive electrode substrate using a YBA-type baker applicator to a basis weight of 15 mg cm in terms of solid content. -2 More than 25mg cm -2 The coating was performed as follows. This was dried in a dryer set 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 obtain the positive electrodes of Examples 1 to 5 and Comparative Examples 1 and 2.

[0095] [Fabrication of energy storage elements] Energy storage devices (all-solid-state batteries) were fabricated using the positive electrodes of the above-described Examples and Comparative Examples. 80 mg of an argyrodite-type sulfide solid electrolyte represented by Li6PS5Cl was inserted into a ceramic powder compactor with an inner diameter of 10 mm as the separator material, and pressure-molded using a uniaxial press at room temperature and 50 MPa for several seconds to form an separator. After releasing the pressure, the prepared positive electrode was placed on one side of the separator, and pressure-molded using a uniaxial press at 160°C and 400 MPa for 5 minutes. After releasing the pressure, indium foil and lithium foil as the negative electrode, and SUS316L foil as the negative electrode substrate, were placed on the side opposite the bonding surface of the positive electrode, and bonded using a uniaxial press at room temperature and 50 MPa for several seconds. The resulting mixture was removed from the powder compactor to obtain the energy storage devices (all-solid-state batteries) of Examples 1 to 5 and Comparative Examples 1 and 2. The positive electrode and the electricity storage element were prepared in a glove box in an argon atmosphere with a dew point of −70° C. or lower.

[0096] [evaluation] (Various rate discharge tests) Each of the energy storage elements of the Examples and Comparative Examples was subjected to a discharge test at various rates at 25° 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 provided. 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 provided. These charge and discharge processes constitute one cycle, and three cycles were repeated. The discharge capacity at the third cycle was taken as the discharge capacity at a discharge current of 0.1 C. 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 until 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 percentage of the discharge capacity at a discharging current of 1.0 C relative to the discharge capacity at a discharging current of 0.1 C was calculated, and this was defined as the 1 C / 0.1 C discharge capacity retention rate.

[0097] (Charge-discharge cycle test) A charge-discharge cycle test was carried out on each of the energy storage elements of the Examples and Comparative Examples at 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. Charging was terminated when the charging current reached 0.025 C. After that, a 10-minute rest period was 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. After that, a 10-minute rest period was allowed. These charging and discharging processes constitute one cycle, and three cycles were repeated. Next, 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. The charge was terminated when the charging current reached 0.05 C. A 10-minute rest period was then provided. 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 then provided. These charge and discharge steps constitute one cycle, and were repeated 50 times. The discharge capacity at the 50th cycle was divided by the discharge capacity at the first cycle to determine the discharge capacity retention rate after 50 cycles.

[0098] Table 1 shows the 1C / 0.1C discharge capacity retention rate in the above-mentioned discharge test at each rate and the discharge capacity retention rate after 50 cycles in the charge-discharge cycle test.

[0099] [Table 1]

[0100] As shown in Table 1, Examples 1 to 5, in which the coating layer contained all of lithium, aluminum, and silicon, had a 1C / 0.1C discharge capacity retention rate of 81.0% or more and a discharge capacity retention rate after 50 cycles of 97.0% or more. In contrast, Comparative Example 1 and Comparative Example 2, in which the coating layer did not contain silicon, had a 1C / 0.1C discharge capacity retention rate of less than 81.0% or a discharge capacity retention rate of less than 97.0%. From the above, it was demonstrated that a storage element using a positive electrode active material in which at least a portion of the active material particles are coated with a coating layer consisting essentially of a compound containing lithium, aluminum, silicon, and oxygen can achieve a high 1C / 0.1C discharge capacity retention rate and a high discharge capacity retention rate after 50 cycles. [Industrial Applicability]

[0101] The present invention can be applied to electric storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles. [Explanation of symbols]

[0102] 1 Positive electrode layer 2. Negative electrode layer 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 battery) 20 Energy storage unit 30 Electricity storage device

Claims

1. active material particles containing a lithium transition metal composite oxide; a coating layer that coats at least a portion of the active material particles; and The coating layer is a positive electrode active material for an electricity storage element, which consists essentially of a compound containing lithium, aluminum, silicon and oxygen elements.

2. Obtained by X-ray photoelectron spectroscopy, a molar ratio of lithium element to the sum of aluminum element and silicon element is 1.0 or more; the molar ratio of aluminum element to all transition metal elements in the lithium transition metal composite oxide is 0.1 or more; 2. The positive electrode active material for an electricity storage device according to claim 1, wherein the molar ratio of silicon element to the transition metal element is 0.1 or more.

3. A positive electrode comprising the positive electrode active material for an electric storage device according to claim 1 or 2 and a sulfide solid electrolyte.

4. An electric storage element comprising the positive electrode according to claim 3 .

5. The energy storage element according to claim 4, which is an all-solid-state battery.

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