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

Abstract

Each of active material particles according to one aspect of the present invention has an active material matrix and a coating layer that covers at least a part of the surface of the active material matrix; the coating layer contains an oxide that contains lithium atoms and titanium atoms; and the content of the lithium atoms relative to the titanium atoms in the oxide is more than 1 but not more than 4 in terms of the molar ratio.

Description

[Technical Field]

[0001] The present invention relates to active material particles (hereinafter also referred to as positive electrode active material for non-aqueous electrolyte secondary batteries), electrodes (hereinafter also referred to as electrodes for non-aqueous electrolyte secondary batteries), electricity storage elements (hereinafter also referred to as non-aqueous electrolyte secondary batteries), all-solid-state secondary batteries (hereinafter also referred to as all-solid-state batteries), methods for producing active material particles, and electricity storage devices. [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. In addition to lithium ion secondary batteries, capacitors such as lithium ion capacitors are also widely used as energy storage elements. Energy storage elements using a solid electrolyte as the non-aqueous electrolyte, such as all-solid-state batteries, have also been developed.

[0003] As positive electrode active materials for non-aqueous electrolyte secondary batteries, such as lithium secondary batteries and all-solid-state secondary batteries, those having a material capable of absorbing and releasing lithium ions and further having a material with a different composition or structure on the surface of the material have been studied (see, for example, Patent Documents 1 to 5). In particular, as active materials suitable for all-solid-state batteries, various active material particles whose surfaces are coated with oxides or the like having lithium ion conductivity have been developed.

[0004] Patent Document 1 states, "100 parts by weight of LiCoO2 powder and 0.05 parts by weight of Li2ZrO3 powder were mixed in a solid state, and then heat-treated at 750°C for 5 hours to produce a lithium-cobalt-based positive electrode active material in which Li2ZrO3 was coated on LiCoO2." (Paragraph

[0081] ) The same document also states, "100 parts by weight of LiCoO2 powder and 0.05 parts by weight of Li2TiO3 powder were mixed in a solid state, and then heat-treated at 750°C for 5 hours to produce a lithium-cobalt-based positive electrode active material in which LiCoO2 was coated with Li2TiO3." (Paragraph

[0082] ) The document also states that a positive electrode was produced using the produced positive electrode active material, a porous polyethylene separator was interposed between the positive electrode and the negative electrode to produce an electrode assembly, the electrode assembly was placed inside a battery case, and then an electrolyte was injected into the case to produce a coin cell (paragraphs

[0088] to

[0090] ).

[0005] In Patent Document 2, in Example 1, it is stated that "...a spinel-type composite oxide powder, i.e., the present core particle powder, was obtained." Chemical analysis of the spinel-type composite oxide powder revealed that it contained 4.1 wt% Li, 13.3 wt% Ni, 40.8 wt% Mn, and 5.2 wt% Ti. In other words, the composition formula is Li[Li 0.07 Mn 1.33 Ni 0.41 Ti 0.19 ]O 4-δ where the M1 element corresponds to Ni and the M2 element corresponds to Ti. (Preparation of positive electrode active material) The amounts of lithium ethoxide and pentaethoxyniobium were adjusted so that the molar ratio of Li to Nb (Li / Nb) was 2.0, and these were added to and dissolved in ethanol to prepare a coating sol-gel solution (lithium content: 1.5 mmol, niobium content: 0.75 mmol). Five grams of the spinel-type composite oxide powder (the core particle powder) was added to this coating sol-gel solution, and the solution was heated to 60°C for 30 minutes using a rotary evaporator while irradiating with ultrasound to cause hydrolysis. The pressure was then reduced over 30 minutes while maintaining the temperature at 60°C to remove the solvent, and the solution was then left to dry at room temperature for 16 hours. Next, the solution was calcined in an air atmosphere at 350°C for 5 hours to obtain a positive electrode active material (sample). (Paragraphs

[0090] to

[0091] ) Furthermore, the same document states that, in Example 8, "a positive electrode active material (sample) was obtained in the same manner as in Example 1, except that the amounts of lithium ethoxide and pentaethoxyniobium were changed as shown in Table 4 and tetra-i-propoxytitanium (Ti(Oi-C3H7)4) was added" (paragraph

[0096] ). Table 4 of the same document also states that Example 8 used 3 mmol of lithium ethoxide, 1.4 mmol of pentaethoxyniobium, and 0.1 mmol of tetrapropoxy-i-titanium. Furthermore, the same document describes the positive electrode active material obtained in the example and a sample of a compound having the composition formula: Li 5.8 PS 4.8 Cl 1.2 It is also stated that an all-solid-state battery was produced using a positive electrode composite containing a solid electrolyte powder represented by the formula (paragraphs

[0104] to

[0106] ).

[0006] Patent Document 3 states, "(Preparation of first precursor coating liquid) A first precursor coating liquid (LiNbO3 precursor sol-gel solution) was obtained by mixing 1 mmol of lithium ethoxide (Kojundo Chemical Co., Ltd.) and 1 mmol of pentaethoxyniobium (Kojundo Chemical Co., Ltd.) in 20 ml of ethanol (Wako Pure Chemical Industries, Ltd.). (Preparation of second precursor coating liquid) In 20 ml of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.), 1 mmol of lithium ethoxide (manufactured by Kojundo Chemical Co., Ltd.) and 1 mmol of titanium tetraisopropoxide (manufactured by Kojundo Chemical Co., Ltd.) were mixed to obtain a second precursor coating liquid (Li2Ti2O5 precursor sol-gel solution). (Formation of lithium ion conductive layer) A lithium cobalt oxide thin film (positive electrode active material) was obtained on a gold substrate by sputtering. The first precursor coating liquid was applied to the surface of the lithium cobalt oxide thin film, dried, and then baked at 350°C for 0.5 hours to obtain a 5-nm-thick lithium ion conductive layer. (Formation of stabilizing layer) The second precursor coating liquid was applied onto the surface of the lithium ion conductive layer, dried, and then baked at 350°C for 0.5 hours to obtain a stabilizing layer with a thickness of 5 nm. (Formation of reaction suppression part) By the above-described steps of forming the lithium ion conductive layer and the above-described stabilizing layer, a reaction suppression part having two layers, the lithium ion conductive layer on the active material side and the stabilizing layer on the solid electrolyte side, was formed on the surface of the positive electrode active material, thereby obtaining an electrode having a positive electrode active material with a reaction suppression part formed on its surface. (Fabrication of all-solid-state batteries) "50 mg of 75Li2S-25P2S5 was placed into the cylinder inside the small cell and pressed with the upper and lower pistons to form a solid electrolyte. Next, the above-mentioned electrode was pressed onto the solid electrolyte layer in the same manner to form a positive electrode active material layer. Subsequently, Li-In foil was pressed onto the side of the solid electrolyte layer opposite the side on which the positive electrode active material layer was formed in the same manner to form a negative electrode active material layer, thereby obtaining a power generating element. Next, the bolts of the small cell were tightened, wiring was connected, and a desiccant was placed inside the glass cell before assembly to produce an all-solid-state battery." (Paragraphs

[0098] to

[0103] )

[0007] In Patent Document 4, in Example 1, it is stated that "spherical Ni particles were prepared by the co-precipitation method." 0.92 Co 0.08 (OH)2 hydroxide precursor was synthesized. The hydroxide precursor was mixed with a Li-containing raw material LiOH and an Al-containing raw material Al2O3 using a mixer, and the mixture was heated in a sintering furnace under an O2 atmosphere at a rate of 1°C per minute to 350°C for 4 hours, then heated at a rate of 2°C per minute to a heat treatment temperature of 650°C for 10 hours, and then naturally cooled. The resulting positive electrode active material was mixed with a W-containing raw material (WO3) using a mixer. The mixture was heated in the same sintering furnace under an O2 atmosphere at a rate of 2°C per minute to a heat treatment temperature of 600°C for 5 hours, and then naturally cooled. Next, the heat treatment and cooling were carried out once more under the same conditions as above. The positive electrode active material prepared in Example 1 contained Li 1.0 Ni 0.902 Co 0.079 Al 0.014 W 0.005 O2 composition formula.' (Paragraphs

[0100] to

[0101] ) The same document also states that, 1.04 Ni 0.901 Co 0.078 Al 0.014 W 0.005 Ti 0.001 Zr 0.001 The document also states, "The positive electrode active material of Example 7 was prepared in the same manner as in Example 1, except that a W-containing raw material (WO3), a Ti-containing raw material (TiO2), and a Zr-containing raw material were mixed together to form a positive electrode active material having a composition formula of 02.02." (Paragraph

[0107] ) The document also states, "Figures 10 to 12 are graphs showing the XRD analysis results for the positive electrode active materials prepared in Examples 5 to 7. ... 12, it can be seen that a positive electrode active material with an NCA composition was formed, and at the same time, it was confirmed that peaks corresponding to Li4WO5, Li6WO6, LiTiO2, Li4TiO4, and Li4ZrO4 were present in the positive electrode active material.' (Paragraphs

[0132] to

[0135] ) Furthermore, the same document also states that a positive electrode was manufactured using the positive electrode active materials manufactured in the examples and comparative examples, and an electrolyte was injected into a separator interposed between the positive electrode and the negative electrode to manufacture a lithium secondary battery (Paragraphs

[0141] to

[0143] ).

[0008] Patent Document 5 states, "(1) Coated active material (B-1): Synthesis of oxide Ti coated NCA Add 600 mL of dehydrated ethanol to a 2 L flask, add 0.26 g (5 mmol) of ethoxylithium, 1.42 g (5 mmol) of titanium tetraisopropoxide, and 0.5 g (5 mmol) of acetylacetone, and stir under a nitrogen atmosphere to prepare LTO (Li4Ti5O 12 ) sol was formed. 0.85 Co 0.10 Al 0.05 208 g of O2 was added and stirred for 30 minutes at 25°C in a nitrogen atmosphere. After removing the ethanol under reduced pressure at 50°C, the obtained powder was baked at 350°C for 30 minutes and further dried at 120°C for 4 hours to obtain an active material NCA coated with LTO (hereinafter abbreviated as LTO-coated NCA; the same applies to the following coated active materials) as coated active material (B-1). (2) Coated active material (B-2): Synthesis of Zr oxide-coated NCA "(Paragraph

[0124] ) The document states that, "An LZO (Li2ZrO3)-coated NCA was obtained as coated active material (B-2) in the same manner as in the synthesis of (1) coated active material (B-1) above, except that the titanium tetraisopropoxide was replaced with zirconium tetrapropoxide and the dehydrated ethanol was replaced with dehydrated propanol." The document also states that a solid electrolyte composition was prepared using the synthesized coated active material, a positive electrode sheet for an all-solid-state secondary battery was produced from the solid electrolyte composition, and an all-solid-state secondary battery was produced using the positive electrode sheet (Paragraphs

[0125] to

[0127] ,

[0130] ,

[0137] ).

[0009] Patent Document 6 describes a method for converting LiCoO2, a positive electrode active material, into Li4Ti5O 12 An all-solid-state lithium battery is described in which a material coated with the above is used in the positive electrode. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Special Publication No. 2020-537319 [Patent Document 2] WO2018 / 012522 [Patent Document 3] WO2013 / 046443 [Patent Document 4] Japanese Patent Publication No. 2020-31052 [Patent Document 5] WO2018 / 043382 [Patent Document 6] Japanese Patent Application Laid-Open No. 2011-165467 Summary of the Invention [Problem to be solved by the invention]

[0011] Positive electrode active materials that have a material capable of absorbing and releasing lithium ions and, on the surface thereof, a material with a different composition or structure from the material have had the problem that, when used in a non-aqueous electrolyte secondary battery, the battery capacity during high-rate discharge is significantly reduced.

[0012] Li4Ti5O 12 Even in an energy storage element using conventional active material particles whose surfaces are coated with, for example, an increase in resistance occurs with the charge-discharge cycle. Since an increase in the resistance of an energy storage element leads to a decrease in output, it is desirable that the resistance does not increase even when the element is repeatedly charged and discharged.

[0013] The present invention has been made in light of the above circumstances, and its object is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that suppresses a decrease in battery capacity during high-rate discharge even when the battery has a surface having a material of a different composition or structure, an electrode for a non-aqueous electrolyte secondary battery using the positive electrode active material, and a non-aqueous electrolyte secondary battery, particularly an all-solid-state secondary battery, using the electrode; active material particles that can suppress an increase in resistance associated with charge-discharge cycles of an electricity storage element, an electrode and an electricity storage element using such active material particles, and a method for producing such active material particles. Furthermore, an electricity storage device using such an electricity storage element, non-aqueous electrolyte secondary battery, or all-solid-state secondary battery is also provided. [Means for solving the problem]

[0014] The active material particles according to one aspect of the present invention include an active material base (hereinafter also referred to as the base) and a coating layer (hereinafter also referred to as the surface layer) that covers at least a part of the surface of the active material base. The coating layer contains a composite oxide containing lithium atoms and titanium atoms, and the content of the lithium atoms with respect to the titanium atoms in the composite oxide is more than 1 and 4 or less in terms of molar ratio.

[0015] The positive electrode active material for a non-aqueous electrolyte secondary battery according to another aspect of the present invention includes a base material composed of a material capable of occluding and releasing lithium ions, and a surface layer that exists on the surface of the base material and contains each element of lithium, titanium, oxygen, and at least one element (A 2 element) that becomes a monovalent cation of 5 or more valences. When the molar ratio of the titanium to the A 2 element is Ti:A 2 =(1 - x2):x2, it is provided with a surface layer that satisfies 0 < x2 ≤ 0.5.

[0016] The positive electrode active material for a non-aqueous electrolyte secondary battery according to another aspect of the present invention includes a base material composed of a material capable of occluding and releasing lithium ions, and a surface layer that exists on the surface of the base material and contains each element of lithium, titanium, oxygen, and at least one element (A 3 element) that becomes a tetravalent monovalent cation whose ionic radius exceeds 0.0605 nm when the coordination number is 6.

[0017] 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 a non-aqueous electrolyte secondary battery according to one aspect of the present invention and a solid electrolyte.

[0018] The electrode for a non-aqueous electrolyte secondary battery according to another aspect of the present invention includes the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present invention.

[0019] The power storage element according to another aspect of the present invention includes the electrode according to one aspect of the present invention.

[0020] A non-aqueous electrolyte secondary battery according to another aspect of the present invention includes the electrode according to the aspect of the present invention.

[0021] An all-solid-state secondary battery according to another aspect of the present invention includes the electrode according to the aspect of the present invention and a solid electrolyte.

[0022] A method for producing active material particles according to one aspect of the present invention comprises, in this order, coating at least a portion of the surface of a particulate active material base material with a coating agent containing lithium atoms and titanium atoms, and heat-treating the active material base material coated with the coating agent, wherein the content of the lithium atoms relative to the titanium atoms in the coating agent is greater than 1 and less than or equal to 4 in molar ratio.

[0023] An electricity storage device according to another aspect of the present invention includes two or more electricity storage elements, and includes at least one of the electricity storage element according to the aspect of the present invention, the nonaqueous electrolyte secondary battery according to the aspect of the present invention, and the all-solid-state secondary battery according to the aspect of the present invention. [Effects of the Invention]

[0024] According to one aspect of the present invention, there are provided a positive electrode active material for a non-aqueous electrolyte secondary battery that suppresses a decrease in battery capacity during high-rate discharge even when the positive electrode active material has a material with a different composition or structure on its surface, an electrode for a non-aqueous electrolyte secondary battery that uses the positive electrode active material, and a non-aqueous electrolyte secondary battery, particularly an all-solid-state secondary battery, that uses the electrode; active material particles that can suppress an increase in resistance associated with charge-discharge cycles of an electricity storage element, an electrode and an electricity storage element that use such active material particles, and a method for producing such active material particles. Furthermore, there is also provided an electricity storage device that uses such an electricity storage element, a non-aqueous electrolyte secondary battery, or an all-solid-state secondary battery. [Brief explanation of the drawings]

[0025] [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

[0026] First, an outline of the active material particles, electrode, electricity storage element, nonaqueous electrolyte secondary battery, all-solid-state secondary battery, method for producing active material particles, and electricity storage device disclosed in this specification will be described.

[0027] Active material particles (a) according to one aspect of the present invention have 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 a composite oxide containing lithium atoms and titanium atoms, and the content of the lithium atoms relative to the titanium atoms in the composite oxide is greater than 1 and not greater than 4 in molar ratio.

[0028] The active material particles (a) can suppress the increase in resistance that occurs with the charge-discharge cycle of the energy storage device. The reason for this effect is unclear, but the following reason is presumed. As shown in Table 1, Li 4 / 3 Ti 5 / 3 Lithium-ion conductive composite oxides, such as Li2TiO3 and Li4TiO4, which are used as coating materials for conventional active material particles and are also used in the comparative examples described below, have relatively high theoretical densities. In contrast, composite oxides containing lithium and titanium atoms, such as Li2TiO3 and Li4TiO4 in Table 1, where the lithium atom content relative to titanium atom content (Li / Ti) is greater than 1 and less than 4 in molar ratio, have low theoretical densities. For a coating layer of the same mass and thickness, a lower coating layer density allows for a larger surface area of ​​the active material substrate to be coated, reducing the exposed area of ​​the active material substrate and resulting in a more uniform coating layer. Therefore, it is believed that the active material particles (a) have a low theoretical density, which allows for the formation of a more uniform coating layer, thereby suppressing the increase in resistance associated with charge / discharge cycles of the energy storage device. The theoretical densities listed in Table 1 are based on the data in the crystal structure database "Materials Project" (https: / / materialsproject.org / ).

[0029] [Table 1]

[0030] The upper limit of the content of the coating layer relative to the content of the active material base material is preferably 1.2% by mass, more preferably 0.8% by mass, and even more preferably 0.5% by mass. The lower limit of the content of the coating layer relative to the content of the active material base material is preferably 0.001% by mass, more preferably 0.01% by mass. The active material particles (a) can sufficiently cover the active material base material even when the content of the coating layer is relatively small, thereby sufficiently suppressing an increase in resistance associated with charge-discharge cycles of the energy storage device. Furthermore, by setting the content of the coating layer to be equal to or less than the upper limit or equal to or more than the lower limit, the discharge capacity, charge-discharge efficiency, capacity retention rate, etc. of the energy storage device tend to be improved.

[0031] The composite oxide is preferably represented by the following formula 1. Li x1 TiO y A 0 z 1 In formula 1, A 0 represents one or more elements other than Li, Ti, and O. x1 is a number greater than 1 and equal to or less than 4. y is a number greater than 2 and equal to or less than 4. z is a number greater than 0 and equal to or less than 1. In this case, the increase in resistance due to the charge / discharge cycle of the energy storage element can be further suppressed.

[0032] A positive electrode active material (b) for a non-aqueous electrolyte secondary battery according to another aspect of the present invention comprises a base material made of a material capable of absorbing and releasing lithium ions, and at least one element (A) present on the surface of the base material and capable of forming a monatomic cation containing lithium, titanium, oxygen, and a valence of five or more. 2 element), and the titanium and the A 2 The mole ratio of the element is Ti:A 2When it is set as (1 - x2):x2, it has a surface layer satisfying 0 < x2 ≤ 0.5. According to this positive electrode active material (b) for a non-aqueous electrolyte secondary battery, even if it has substances with different compositions or structures on the surface, a non-aqueous electrolyte secondary battery with suppressed decrease in battery capacity during high-rate discharge can be obtained.

[0033] The positive electrode active material (c) for a non-aqueous electrolyte secondary battery according to another embodiment of the present invention (hereinafter, also referred to as "another present embodiment") is composed of a base material capable of occluding and releasing lithium ions, and exists on the surface of the base material, and at least one element (A 3 element) including each element of a tetravalent monatomic cation having an ionic radius exceeding 0.0605 nm when the coordination number is 6, lithium, titanium, and oxygen. According to this positive electrode active material (c) for a non-aqueous electrolyte secondary battery, even if it has substances with different compositions or structures on the surface, a non-aqueous electrolyte secondary battery with suppressed decrease in battery capacity during high-rate discharge can be obtained.

[0034] The electrode (a) according to another aspect of the present invention contains the active material particles (a) according to one aspect of the present invention, the positive electrode active material (b) for a non-aqueous electrolyte secondary battery according to another aspect of the present invention, or the positive electrode active material (c) for a non-aqueous electrolyte secondary battery according to another aspect of the present invention, and a solid electrolyte. Since the electrode (a) contains the active material particles (a) according to one aspect of the present invention, the positive electrode active material (b) for a non-aqueous electrolyte secondary battery according to another aspect of the present invention, or the positive electrode active material (c) for a non-aqueous electrolyte secondary battery according to another aspect of the present invention, an increase in resistance associated with charge and discharge cycles of the power storage element or even if it has substances with different compositions or structures on the surface, a decrease in battery capacity during high-rate discharge can be suppressed.

[0035] A non-aqueous electrolyte secondary battery electrode (b) according to another aspect of the present invention includes the non-aqueous electrolyte secondary battery positive electrode active material (b) according to one aspect of the present invention or the non-aqueous electrolyte secondary battery positive electrode active material (c) according to another aspect of the present invention. Because the electrode (b) contains the non-aqueous electrolyte secondary battery positive electrode active material (b) according to one aspect of the present invention or the non-aqueous electrolyte secondary battery positive electrode active material (c) according to another aspect of the present invention, it is possible to suppress a decrease in battery capacity during high-rate discharge of an energy storage device, even if the electrode (b) has a material with a different composition or structure on its surface.

[0036] An energy storage element according to another aspect of the present invention includes the electrode (a) according to the aspect of the present invention or the electrode (b) for a non-aqueous electrolyte secondary battery according to the other aspect of the present invention. Because the energy storage element includes the electrode (a) containing the active material particles (a) according to the aspect of the present invention, or the electrode (b) including the positive electrode active material for a non-aqueous electrolyte secondary battery (b) according to the aspect of the present invention or the positive electrode active material for a non-aqueous electrolyte secondary battery (c) according to the other aspect of the present invention, the energy storage element is prevented from increasing in resistance with charge / discharge cycles or from decreasing in battery capacity during high-rate discharge even if the element has a material with a different composition or structure on its surface.

[0037] A nonaqueous electrolyte secondary battery according to another aspect of the present invention includes an electrode (a) according to one aspect of the present invention or an electrode (b) for a nonaqueous electrolyte secondary battery according to another aspect of the present invention. Because the nonaqueous electrolyte secondary battery includes an electrode (a) containing active material particles (a) according to one aspect of the present invention, or an electrode (b) comprising a positive electrode active material for a nonaqueous electrolyte secondary battery (b) according to one aspect of the present invention, or a positive electrode active material for a nonaqueous electrolyte secondary battery (c) according to another aspect of the present invention, the nonaqueous electrolyte secondary battery is prevented from increasing in resistance with charge / discharge cycles or from decreasing in battery capacity during high-rate discharge, even if the battery has a material with a different composition or structure on its surface.

[0038] An all-solid-state secondary battery according to another aspect of the present invention includes the electrode (a) according to the aspect of the present invention or the electrode (b) for a non-aqueous electrolyte secondary battery according to the other aspect of the present invention. Because the all-solid-state secondary battery includes the electrode (a) containing the active material particles (a) according to the aspect of the present invention, or the electrode (b) including the positive electrode active material for a non-aqueous electrolyte secondary battery (b) according to the aspect of the present invention, or the positive electrode active material for a non-aqueous electrolyte secondary battery (c) according to the other aspect of the present invention, the all-solid-state secondary battery is prevented from increasing in resistance with charge / discharge cycles or from decreasing in battery capacity during high-rate discharge even if the battery has a material with a different composition or structure on its surface.

[0039] A method for producing active material particles according to one aspect of the present invention comprises, in this order, coating at least a portion of the surface of a particulate active material base material with a coating agent containing lithium atoms and titanium atoms, and heat-treating the active material base material coated with the coating agent, wherein the content of the lithium atoms relative to the titanium atoms in the coating agent is greater than 1 and less than or equal to 4 in molar ratio.

[0040] According to this manufacturing method, it is possible to manufacture active material particles that can suppress an increase in resistance that occurs with charge-discharge cycles of an energy storage device.

[0041] An electricity storage device according to one aspect of the present invention includes two or more electricity storage elements, and at least one of the nonaqueous electrolyte electricity storage element according to the above-described aspect of the present invention, a nonaqueous electrolyte secondary battery, and an all-solid-state secondary battery. Because the electricity storage device includes at least one of the nonaqueous electrolyte electricity storage element according to the above-described aspect of the present invention, a nonaqueous electrolyte secondary battery, and an all-solid-state secondary battery, an increase in resistance due to charge / discharge cycles or a decrease in battery capacity during high-rate discharge is suppressed even if the battery has a surface containing a substance with a different composition or structure.

[0042] Hereinafter, active material particles and a manufacturing method thereof, an electrode, a power storage element, a nonaqueous electrolyte secondary battery, an all-solid-state secondary battery and a manufacturing method thereof, a power storage device, and other embodiments according to one embodiment of the present invention will be described in detail. The names of the components (components) used in each embodiment may differ from the names of the components (components) used in the background art. In this specification, the term "nonaqueous electrolyte secondary battery" refers to a secondary battery that uses an electrolyte that does not contain water. Therefore, the term "nonaqueous electrolyte secondary battery" in this specification includes all-solid-state secondary batteries that use a solid electrolyte and nonaqueous electrolyte secondary batteries that use a nonaqueous electrolyte in which an electrolyte salt is dissolved in a solvent other than water (nonaqueous solvent).

[0043] <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.

[0044] (active material base material) The active material matrix serves as the core of the active material. The matrix may be in the form of particles or a film. When the matrix is ​​in the form of particles, only particles composed of one of the above materials may be used, or a mixture of two or more particles composed of different materials may be used. 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 particles essentially composed of the active material alone, or may be particles composed of the active material alone. The active material matrix may be primary particles composed 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.

[0045] 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.

[0046] 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 nonaqueous electrolyte secondary batteries with excellent output characteristics to be obtained at low cost. In particular, lithium transition metal composite oxides having an α-NaFeO2-type crystal structure containing Co are particularly preferred because they allow nonaqueous electrolyte secondary batteries with even better output characteristics to be obtained.

[0047] 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.

[0048] In formula 2, Me is preferably substantially composed of the three elements Ni, Co, and Mn, although Me may contain other metals.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] "Graphite" refers to a graphite material 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.

[0058] "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.

[0059] 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.

[0060] "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.

[0061] "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.

[0062] The average particle size of the active material base material can be, for example, 0.001 μm or more and 100 μm or less, or 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.

[0063] 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.

[0064] (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 suppress an increase in resistance accompanying the charge / discharge cycles of the energy storage device.

[0065] The coating layer contains a composite oxide containing lithium atoms and titanium atoms. The content of the composite oxide 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 the composite oxide. Components other than the oxides that may be contained in the coating layer include oxides other than the oxides mentioned above, nitrides, sulfides, halides, etc.

[0066] The composite oxide contained in the coating layer of the active material particles (a) according to one embodiment of the present invention has a molar ratio of lithium atoms to titanium atoms (Li / Ti) of more than 1 and not more than 4. The lower limit of the lithium atom content to titanium atoms (Li / Ti) is preferably 1.5, and in some cases, more preferably 2. On the other hand, the upper limit of the lithium atom content to titanium atoms (Li / Ti) is preferably 3.5, more preferably 3, and in some cases, even more preferably 2.5 or 2. When the lithium atom content to titanium atoms (Li / Ti) is not less than the above lower limit or not more than the above upper limit, a highly uniform coating layer made of this composite oxide is more likely to be formed, even if the amount of the composite oxide is relatively small relative to the active material base material.

[0067] The composite oxide may contain atoms other than lithium, titanium, and oxygen atoms. Examples of other atoms include typical nonmetal atoms such as B, C, N, S, P, F, Cl, Br, and I; typical metal atoms such as Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal atoms such as Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, and W. However, the total content of lithium, titanium, and oxygen atoms relative to all atoms constituting the composite oxide is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 99 mol% or more. The composite oxide may be composed of lithium, titanium, and oxygen atoms.

[0068] The composite oxide is preferably represented by the following formula 1. Li x1 TiO y A 0 z 1 In formula 1, A 0 represents one or more elements other than Li, Ti, and O. x1 is a number greater than 1 and equal to or less than 4. y is a number greater than 2 and equal to or less than 4. z is a number greater than 0 and equal to or less than 1.

[0069] A in Equation 1 0 Examples of such elements include typical non-metallic elements such as B, C, N, S, P, 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, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, and W.

[0070] In formula 1, the lower limit of x1 is preferably 1.5, and in some cases more preferably 2. The upper limit of x1 is preferably 3.5, more preferably 3, and in some cases even more preferably 2.5 or 2. When x1 is equal to or greater than the above lower limit or equal to or less than the above upper limit, even if the amount of the composite oxide is relatively small relative to the active material base material, a highly uniform coating layer made of this composite oxide is more likely to be formed.

[0071] In formula 1, the lower limit of y is preferably 2.5, and in some cases more preferably 3. The upper limit of y is preferably 3.5, and in other cases more preferably 3. When y is equal to or greater than the above lower limit or equal to or less than the above upper limit, the structure of the complex oxide is stabilized, and an increase in resistance due to charge / discharge cycles of the energy storage element can be further suppressed.

[0072] In formula 1, z 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 z is equal to or less than the above upper limit, the stability of the complex oxide structure is increased, and an increase in resistance due to charge / discharge cycles of the energy storage element can be further suppressed.

[0073] Specific examples of the composite oxide include Li2TiO3 and Li4TiO4.

[0074] The composite oxide 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.

[0075] The content of the coating layer relative to the content of the active material matrix may be 0.01% by mass or more and 2% by mass or less. The upper limit of the content of the coating layer relative to the content of the active material matrix is ​​preferably 0.5% by mass, more preferably 0.3% by mass, and in some cases, 0.2% by mass or 0.15% by mass is even more preferable. With these active material particles, even when the content of the coating layer is in this relatively low range, it is possible to sufficiently suppress the increase in resistance associated with the charge-discharge cycles of the energy storage device. Furthermore, by setting the content of the coating layer to the above upper limit or less, the discharge capacity, charge-discharge efficiency, and capacity retention rate after charge-discharge cycles of the energy storage device tend to be improved. Furthermore, by setting the content of the coating layer to the above upper limit or less, the content ratio of the active material matrix increases relatively, thereby increasing the energy density of the energy storage device. The lower limit of the content of the coating layer relative to the content of the active material matrix is ​​preferably 0.03% by mass, more preferably 0.05% by mass, even more preferably 0.1% by mass, and in some cases, even more preferably 0.15% by mass. By setting the content of the coating layer to the above lower limit or more, a sufficient amount of coating layer is formed on the active material base material, and an increase in resistance due to charge / discharge cycles of the energy storage element can be sufficiently suppressed.

[0076] 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 1 μm or even 1 μm. The upper limit of the average particle size of the active material particles may be 20 μm or even 5 μm.

[0077] The surface of the base material of the positive electrode active material (b) for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention contains lithium, titanium, oxygen, and at least one element (A) that becomes a monatomic cation with a valence of five or more. 2 There is a surface layer containing titanium and A. 2When the molar ratio of the element to Ti:A 2 =(1 - x2):x2, it satisfies 0 < x2 ≤ 0.5. Here, the element that becomes a monovalent cation of pentavalent or higher means an element that produces a monovalent cation of pentavalent or higher, the ionic radius of which is reported by Schannon et al. (Acta Cryst. A 32 (1976) 751). That is, "present on the surface of the base material, containing each element of lithium, titanium, oxygen, and at least one element (A 2 element) that becomes a monovalent cation of pentavalent or higher, and when the molar ratio of the titanium to the A 2 element is Ti:A 2 =(1 - x2):x2, the surface layer that satisfies 0 < x2 ≤ 0.5" can be rephrased as "present on the surface of the base material, containing each element of lithium, titanium, oxygen, and at least one element (A 2 element) that produces a monovalent cation of pentavalent or higher, the ionic radius of which is reported by Schannon et al. (Acta Cryst. A 32 (1976) 751), and when the molar ratio of the titanium to the A 2 element is Ti:A 2 =(1 - x2):x2, the surface layer that satisfies 0 < x2 ≤ 0.5".

[0078] According to this surface layer, even if the surface has substances with different compositions or structures, the decrease in battery capacity during high-rate discharge is suppressed. This phenomenon is推测 to occur by the following mechanism. In the surface layer containing each element of lithium, titanium, oxygen, and at least one element (A 2 element) that becomes a monovalent cation of pentavalent or higher, and when the molar ratio of the titanium to the A 2 element is Ti:A 2 =(1 - x2):x2 and satisfies 0 < x2 ≤ 0.5, Li2TiO3 contains Li2(Ti 2 A 1-x2 A 2 x2 )O 3+α as the main component, in which part of the Ti is substituted by the A 2In element-free Li2TiO3, Ti exists only in +4 valence, while in Li2(Ti 1-x2 A 2 x2 )O 3+α So, A exists with a valence of +5 or more, which is larger than Ti. 2 Because the battery contains elements, charge compensation causes some of the Ti to become +3 or less valent. The occurrence of this +3 or less valent Ti increases electronic conductivity compared to when Ti exists only in a +4 valent state, reducing resistance in the surface layer and suppressing the decrease in battery capacity during high-rate discharge. The lower limit of the value of x2 is preferably 0.05 or more, more preferably 0.10 or more. When the value of x2 is equal to or more than the lower limit, the decrease in battery capacity during high-rate discharge is significantly suppressed. On the other hand, the upper limit of the value of x2 is preferably 0.45 or less, more preferably 0.40 or less. When the value of x2 is equal to or less than the upper limit, the LiA 2 O 3+β For these reasons, the value of x2 is preferably 0.05 or more and 0.45 or less, and more preferably 0.10 or more and 0.40 or less.

[0079] The surface of the base material of the positive electrode active material (c) for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention contains at least one element (A) that is a tetravalent monoatomic cation having an ionic radius of more than 0.0605 nm when the coordination number is 6, selected from the group consisting of lithium, titanium, oxygen, and arsenic. 3 There is a surface layer containing lithium, titanium, oxygen, and at least one element (A) that forms a tetravalent monoatomic cation with an ionic radius of more than 0.0605 nm when the coordination number is six. Here, the term "at least one element that forms a tetravalent monoatomic cation with an ionic radius of more than 0.0605 nm when the coordination number is six" refers to an element reported by Schannon et al. (Acta Cryst. A 32 (1976) 751) as a tetravalent monoatomic cation with an ionic radius of more than 0.0605 nm when the coordination number is six. That is, "the surface layer contains lithium, titanium, oxygen, and at least one element (A) that forms a tetravalent monoatomic cation with an ionic radius of more than 0.0605 nm when the coordination number is six." 3The term "surface layer containing lithium, titanium, and oxygen present on the surface of the base material, as well as elements (A) reported by Schannon et al. (Acta Cryst. A 32 (1976) 751) to have tetravalent monoatomic cations with six-coordinated ions and an ionic radius of more than 0.0605 nm" refers to a surface layer containing lithium, titanium, and oxygen present on the surface of the base material. 3 This can be rephrased as "a surface layer containing each of the elements (elements)."

[0080] This surface layer suppresses the decrease in battery capacity during high-rate discharge even if the surface has a material with a different composition or structure. This phenomenon is presumed to occur due to the following mechanism. The constituent elements are lithium, titanium, oxygen, and at least one element (A) that forms a tetravalent monoatomic cation with an ionic radius of more than 0.0605 nm when the coordination number is 6. 3 In the surface layer containing each element, a part of Ti in Li2TiO3 is converted into A. 3 Li2(Ti), an oxide substituted with elements 1-x3 A 3 x3 )O3 as the main component. Li2TiO3 and Li2(Ti 1-x3 A 3 x3 )O3, Ti and A 3 The element is located as a tetravalent monoatomic cation in an octahedron with six oxygen atoms at the vertices. According to the report by Schannon et al. mentioned above, the ionic radius of +tetravalent Ti surrounded by six oxygen atoms (hexacoordinated) is 0.0605 nm. Then, Li2(Ti 1-x3 A 3 x3 )O3, Ti 4+ A part of the ionic radius is larger than this 4+ The substitution of these large ions results in the formation of Li in the lattice. + Weakening the interaction between Li and other ions + or by expanding the lattice volume to accommodate Li + It is believed that by increasing the conductive path, the lithium ion conductivity of the surface layer is increased, thereby suppressing the decrease in battery capacity during high-rate discharge. The lower limit of the value of x3 is preferably 0.05 or more, and more preferably 0.1 or more. When the value of x3 is equal to or greater than the lower limit, the decrease in battery capacity during high-rate discharge is significantly suppressed. On the other hand, the upper limit of the value of x3 is preferably 0.9 or less, and more preferably 0.7 or less. When the value of x3 is equal to or less than the upper limit, the decrease in battery capacity due to repeated charge and discharge is effectively suppressed. For these reasons, the value of x3 is preferably 0.05 or more and 0.9 or less, and more preferably 0.1 or more and 0.7 or less.

[0081] Furthermore, the surface layer exhibits an even more beneficial effect when the positive electrode active material for a nonaqueous electrolyte secondary battery according to this embodiment or another embodiment is applied to an all-solid-state secondary battery including a sulfide solid electrolyte (hereinafter also referred to as a sulfide-based solid electrolyte) described below. It has been reported that in such all-solid-state secondary batteries, the battery capacity decreases with repeated charge and discharge. This decrease in battery capacity is believed to be due to a reaction between the positive electrode active material and the solid electrolyte, for example, a substitution reaction between oxygen in the positive electrode active material and sulfur in the solid electrolyte. However, the presence of the surface layer on the surface of the positive electrode active material can suppress the decrease in battery capacity due to repeated charge and discharge. This is presumably because the surface layer suppresses the substitution reaction between oxygen and sulfur, thereby suppressing an increase in the interfacial resistance between the positive electrode active material and the sulfide solid electrolyte. This effect of suppressing the decrease in battery capacity becomes more pronounced when a sulfide solid electrolyte is combined with a base material made of a lithium transition metal composite oxide, becomes even more pronounced when a sulfide solid electrolyte is combined with a base material made of a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, and becomes even more pronounced when a sulfide solid electrolyte is combined with a base material made of a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure that contains cobalt as a transition metal element.

[0082] A contained in the surface layer 2As the element, it is preferably at least one selected from niobium (Nb), molybdenum (Mo), tantalum (Ta), and tungsten (W). These elements generate a monovalent cation of pentavalent or higher having an ionic radius close to that of Ti 4+ and result in a Li2(Ti 1-x2 A 2 x2 )O 3+α with excellent electrochemical stability.

[0083] The surface layer preferably has a composition formula Li a2 (Ti 1-x2 A 2 x2 ) b2 O c2 (where A 2 is at least one element that becomes a monovalent cation of pentavalent or higher, and a2, b2, and c2 are real numbers satisfying 1 < a2 < 4, 1 ≤ b2 < 2, and 2 < c2 < 4, respectively). When the surface layer has the above composition formula, the content ratio of Li2(Ti 1-x2 A 2 x2 )O 3+α becomes high, and the effect of suppressing the decrease in battery capacity during high-rate discharge becomes remarkable.

[0084] As the element A 3 contained in the surface layer, those that become a tetravalent monovalent cation with an ionic radius of 0.061 nm or more and 0.090 nm or less when the coordination number is 6 are preferable, and those with an ionic radius of 0.062 nm or more and 0.070 nm or less are more preferable. By setting the ionic radius within the above range, the decrease in battery capacity during high-rate discharge is further suppressed.​​​​​​​​​​​​)This is because O3 has excellent electrochemical stability.

[0086] The above surface layer has a composition formula Li a3 (Ti 1―x3 A 3 x3 ) b3 O c3 (where A 3 is at least one element that is a tetravalent monatomic cation with an ionic radius exceeding 0.0605 nm when the coordination number is 6, and a3, b3, c3, x3 are real numbers satisfying 1 < a3 < 4, 1 ≤ b3 < 2, 2 < c3 < 4, 0 < x3 < 1, respectively). It is preferable that the above surface layer is represented by the above composition formula. When the above surface layer has the above composition formula, the content ratio of Li2(Ti 1-x3 A 3 x3 )O3 becomes high, and the effect of suppressing the decrease in battery capacity during high-rate discharge becomes remarkable.

[0087] Here, the composition of the surface layer in the positive electrode active material for a non-aqueous electrolyte secondary battery is confirmed by the following procedure. For the positive electrode active material, quantitative analysis of elements is performed 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. At this time, for elements that can be quantified by ICP-AES, their content is determined based on the measurement results of ICP-AES. When performing ICP-AES analysis, a sample obtained by completely dissolving the positive electrode active material in an acidic solution by microwave digestion is used as the analysis sample. Next, the crystal structure of the surface layer is confirmed by TEM observation of the surface layer by the method described below. When the surface layer is amorphous, the positive electrode active material is heat-treated so that the surface layer crystallizes, and then the crystal structure of the surface layer is confirmed. From the obtained information, the composition of the surface layer is estimated, and this composition is taken as the composition 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.

[0088] The surface layer is preferably crystalline. Being crystalline, with atoms or ions regularly arranged, provides the surface layer with high electronic conductivity, thereby suppressing a decrease in battery capacity during high-rate discharge. Furthermore, the increased structural stability of the surface layer can improve the capacity retention rate of the nonaqueous electrolyte secondary battery after charge-discharge cycling.

[0089] 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 flake sample, if the active material to be measured is collected by disassembling the energy storage element, nonaqueous electrolyte secondary battery, or all-solid-state secondary battery, the sample is prepared by the following method. The energy storage element, nonaqueous electrolyte secondary battery, 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, nonaqueous electrolyte secondary battery, or all-solid-state secondary battery is disassembled, and the electrode assembly is removed. Next, fragments containing the active material are collected from the removed electrode assembly. Next, the portion of the collected fragment containing the active material is processed into a flake sample using a focused ion beam (FIB) device and subjected to TEM observation.

[0090] However, the active material is a coating agent containing lithium atoms and titanium atoms, a coating agent containing lithium, titanium and A 2 Solutions containing the elements lithium, titanium and A 3 If the active material is manufactured by a method in which a solution containing one of the elements is applied to the substrate and then heated, 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 substrate is heated under the same conditions as when manufacturing the active material to obtain a sample powder. Next, the obtained sample powder is subjected to X-ray diffraction measurement. If peaks derived from the crystalline structure are observed in the obtained X-ray diffraction pattern, the coating layer or surface layer is determined to be crystalline. X-ray diffraction measurement is performed by the following procedure. First, the sample powder to be used for measurement is filled into an X-ray diffraction sample holder. Powder X-ray diffraction measurement is performed using an X-ray diffractometer (Rigaku's "MiniFlex II"). The radiation source is CuKα radiation, the tube voltage is 30 kV, the tube current is 15 mA, and the diffracted X-rays are passed through a 30 μm thick Kβ filter and detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2). 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.

[0091] The amount of the surface layer is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.15% by mass or more, and even more preferably 0.25% 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 0.75% by mass or less, more preferably 0.70% by mass or less, even more preferably 0.65% by mass or less, even more preferably 0.60% by mass or less, and even more preferably 0.45% by mass or less, relative to the base material. Setting the amount of the surface layer at or below the upper limit can suppress a decrease in battery capacity during high-rate discharge when used in a nonaqueous electrolyte secondary battery. Also, for these reasons, the amount of the surface layer is preferably 0.05% by mass or more and 0.75% by mass or less, or 0.05% by mass or more and 0.70% by mass or less, more preferably 0.1% by mass or more and 0.65% by mass or less, even more preferably 0.15% by mass or more and 0.60% by mass or less, and even more preferably 0.25% by mass or more and 0.45% by mass or less, relative to the base material.

[0092] In the positive electrode active material for a non-aqueous electrolyte secondary battery (b) according to this embodiment and the positive electrode active material for a non-aqueous electrolyte secondary battery (c) according to another embodiment, the surface layer preferably exists 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 proportion of the area of ​​the exposed portion to the total surface area of ​​the base material is relatively small and the exposed portion is not unevenly distributed in a specific location on the base material, the positive electrode active material for a non-aqueous electrolyte secondary battery will exhibit the above-mentioned effects. Furthermore, as described above, when two or more types of base material particles composed of different materials are mixed and used, it is sufficient that at least one type of base material particle has a surface layer.

[0093] When the base material is particulate, the average particle size of the positive electrode active material (b) or (c) formed by 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) or (c) to the above lower limit or more, the positive electrode active material is easy to manufacture or handle. By setting the average particle size of the positive electrode active material (b) or (c) to the above upper limit or less, the decrease in battery capacity during high-rate discharge can be suppressed. Note that when a composite of the positive electrode active material (b) or (c) with another material is used, the average particle size of the composite is the average particle size of the positive electrode active material (b) or (c).

[0094] (Application) The active material particles (a), the positive electrode active material for non-aqueous electrolyte secondary batteries (b), and the positive electrode active material for non-aqueous electrolyte secondary batteries (c) can be used in various types of energy storage devices, but are particularly suitable for energy storage devices using solid electrolytes, particularly all-solid-state energy storage devices. When the active material particles are used in an energy storage device using a solid electrolyte, a good interface is formed between the active material particles and the solid electrolyte, and the effect of suppressing an increase in resistance due to charge-discharge cycles is particularly fully exhibited. The active material particles (a), the positive electrode active material for non-aqueous electrolyte secondary batteries (b), and the positive electrode active material for non-aqueous electrolyte secondary batteries (c) can also be applied to energy storage devices using a combination of a solid electrolyte and an electrolytic solution as the electrolyte, as well as energy storage devices using only an electrolytic solution as the electrolyte.

[0095] <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 lithium atoms and titanium atoms; and (2) heat-treating the active material base material coated with the coating agent. Also, a positive electrode active material (b) according to this embodiment comprises a base material containing lithium, titanium, and A atoms. 2 The cathode active material (c) according to another embodiment of the present invention can be suitably produced by applying a solution containing each of the elements to a base material and then heating the applied solution. 3It can be suitably produced by a method in which a solution containing each element is applied and then heated.

[0096] (1) Coating process A conventionally known active material can be used as the particulate active material base material used in this step. For example, 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, the 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.

[0097] The coating agent used in the method for producing active material particles (a) contains lithium atoms and titanium atoms. The coating agent may be, for example, a solution composed of a solute and a solvent. The lithium atoms and titanium atoms are usually contained in the solute component of the coating agent. The molar ratio of the lithium atoms to the titanium atoms in the coating agent is greater than 1 and not greater than 4. The preferred range of the lithium atom content relative to the titanium atoms in the coating agent is the same as the lithium atom content relative to the titanium atoms in the oxide described above.

[0098] The coating agent can be prepared, for example, by dissolving a lithium-containing compound and a titanium-containing compound as solutes in a solvent. A compound containing both lithium and titanium atoms may be used as the solute. Examples of lithium-containing compounds include lithium alkoxides such as lithium ethoxide and lithium methoxide, lithium acetate, and lithium hydroxide. Examples of titanium-containing compounds include titanium alkoxides such as titanium (IV) ethoxide, titanium (IV) methoxide, and titanium (IV) isopropoxide. The mixing ratio of each component is appropriately set depending on the desired composition of the composite oxide. The solvent used in the coating agent is not particularly limited as long as it can dissolve the lithium-containing compound and the titanium-containing compound, but alcohols such as ethanol can be used.

[0099] In addition, lithium, titanium and A 2 Element or A 3 The solution containing each element of the element may be, for example, a lithium-containing compound, a titanium-containing compound, and an A 2 Element-containing compounds or A 3 It can be prepared by dissolving the element-containing compound in a solvent. 2 Element or A 3 Compounds containing two or more of the elements may be used. Examples of lithium-containing compounds include lithium alkoxides such as lithium methoxide and lithium ethoxide, lithium acetate, and lithium hydroxide. Examples of titanium-containing compounds include titanium alkoxides such as titanium (IV) methoxide, titanium (IV) ethoxide, titanium (IV) tetraisopropoxide, and titanium (IV) tetrabutoxide. A 2Examples of element-containing compounds include niobium-containing compounds such as niobium alkoxides, such as niobium (V) ethoxide and niobium (V) methoxide, niobium acetate, and niobium hydroxide, molybdenum-containing compounds such as molybdenum alkoxides, such as molybdenum (V) isopropoxide, tantalum-containing compounds such as tantalum alkoxides, such as tantalum (V) methoxide and tantalum (V) ethoxide, and tungsten-containing compounds such as tungsten alkoxides, such as tungsten (VI) ethoxide. 3 Examples of the element-containing compound include zirconium-containing compounds such as zirconium alkoxides, such as zirconium (IV) ethoxide, zirconium (IV) propoxide, and zirconium (IV) isopropoxide, as well as hafnium-containing compounds such as hafnium (IV) ethoxide and hafnium (IV) isopropoxide monoisopropylate. The mixing ratio of each component is appropriately set depending on the desired composition of the surface layer. The solvent used for the solution includes a lithium-containing compound, a titanium-containing compound, and A. 2 Element-containing compounds or A 3 There are no particular limitations on the solvent as long as it can dissolve the element-containing compound, but for example, ethanol or the like can be used.

[0100] Coating the surface of the active material base material with a coating agent or solution can be performed by conventional coating methods such as spin coating, dip coating, and tumbling fluidized coating. A preferred method involves spraying the solution onto a powder of the base material while fluidizing it. This method allows the solution to be uniformly applied to the surface of the particulate base material. Among these, tumbling fluidized coating is preferred because it facilitates the production of a highly homogeneous 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 tumbling fluidized active material base material and then dried (solvent removal). The temperature inside the tumbling fluidized coating apparatus during tumbling fluidized coating can be, for example, 60°C to 120°C. 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, and the like are preferably used.

[0101] 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.

[0102] (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, a state in which only the solute is present). In the heat treatment step, the coating agent or solution may be dried (solvent removed). Through this heat treatment, the active material particles (a) on which a coating layer containing lithium atoms, titanium atoms, oxygen atoms, and other arbitrary atoms has been formed, and the active material particles (b) on which the coating layer containing lithium atoms, titanium atoms, oxygen atoms, and other arbitrary atoms has been formed are heated. 2 a positive electrode active material for a non-aqueous electrolyte secondary battery (b) having a surface layer containing lithium, titanium, oxygen, A, and other optional elements; 3Thus, a positive electrode active material (c) for a non-aqueous electrolyte secondary battery is obtained, on which a surface layer containing the element and other optional elements is formed.

[0103] The heat treatment is preferably carried out in an oxygen-containing atmosphere, and may be carried out in, for example, an air atmosphere. The lower limit of the heat treatment temperature is, for example, preferably 250°C, more preferably 300°C, and even more preferably 350°C. The upper limit of the heat treatment temperature is preferably 600°C, more preferably 550°C, even more preferably 500°C, and even more preferably 450°C. The lower limit of the heat treatment time is preferably 1 minute, more preferably 10 minutes, and even more preferably 15 minutes. The upper limit of the heat treatment time is preferably 10 hours, more preferably 4 hours, even more preferably 2 hours, and even more preferably 1 hour.

[0104] <Electrode> An electrode (a) according to one embodiment of the present invention contains the active material particles (a) according to one embodiment of the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery (b) or a positive electrode active material for a non-aqueous electrolyte secondary battery (c), and a solid electrolyte. The electrode (a) has a substrate and an active material layer disposed on the substrate directly or via an intermediate layer. The electrode (a) may be a positive electrode or a negative electrode, but is preferably a positive electrode. An electrode (b) according to another embodiment of the present invention contains the positive electrode active material for a non-aqueous electrolyte secondary battery (b) or the positive electrode active material for a non-aqueous electrolyte secondary battery (c) according to one embodiment of the present invention. The electrode (b) has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0105] (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.

[0106] 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).

[0107] 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.

[0108] 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.

[0109] 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.

[0110] (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.

[0111] (active material layer) The active material layer included in the electrode (a) according to one embodiment of the present invention includes the active material particles (a) according to one embodiment of the present invention, the positive electrode active material for a non-aqueous electrolyte secondary battery (b) or the positive electrode active material for a non-aqueous electrolyte secondary battery (c), and a solid electrolyte. The positive electrode active material layer included in the electrode (b) according to another embodiment of the present invention includes the positive electrode active material for a non-aqueous electrolyte secondary battery (b) or the positive electrode active material for a non-aqueous electrolyte secondary battery (c) according to one embodiment of the present invention. The active material layer may contain optional components such as a conductive agent, a binder, a thickener, a filler, etc. The active material layer may be formed from a mixture (positive electrode mixture or negative electrode mixture) containing the active material particles, etc.

[0112] 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.

[0113] When the active material layer contains a solid electrolyte, 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.

[0114] 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.

[0115] 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 energy storage element can be increased.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] <Energy storage element> An energy storage device according to one embodiment of the present invention (hereinafter referred to as a nonaqueous electrolyte secondary battery or simply a "secondary battery") includes an electrode assembly having a positive electrode, a negative electrode, and a separator, and a container for accommodating the electrode assembly. When the nonaqueous electrolyte secondary battery is an all-solid-state secondary battery that includes only a solid electrolyte as the nonaqueous electrolyte, the separator is formed of a separator, and the nonaqueous electrolyte is contained in the electrode assembly. The electrode assembly is typically a stacked type in which multiple positive electrodes and multiple negative electrodes are stacked with separators interposed between them, or a wound type in which positive electrodes and negative electrodes are stacked with separators interposed between them and wound. When the separator is formed of a solid electrolyte, the electrode assembly may 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 following description will be given using an all-solid-state battery as a specific example. The energy storage element 10 of FIG. 1 is an all-solid-state secondary battery, and is a secondary battery in which a positive electrode 1 and a negative electrode 2 are arranged with an isolation layer 3 between them. 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 active material layer 5, and the positive electrode substrate 4 are stacked in this order on the negative electrode substrate 7. At least one of the positive electrode 1 and the negative electrode 2 in the energy storage element 10 is an electrode according to one embodiment of the present invention.

[0126] (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.

[0127] 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.

[0128] (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.

[0129] 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.

[0130] (isolation layer) The separator 3 typically contains a solid electrolyte. Examples of the solid electrolyte contained in the separator 3 include the above-described conventionally known solid electrolytes, such as sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes. Among these, sulfide-based solid electrolytes are preferred because they have high ionic conductivity and are prone to plastic deformation, facilitating the formation of interfaces with the positive electrode active material and the negative electrode active material. The solid electrolyte content 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.

[0131] The isolation layer 3 may contain optional components such as a solid electrolyte, a phosphate compound such as LiPO, an oxide, a halogen compound, a binder, a thickener, and a filler. 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.

[0132] The lower limit of the average thickness of the isolating layer 3 is preferably 1 μm, more preferably 3 μm. The upper limit of the average thickness of the isolating layer 3 is preferably 200 μm, preferably 100 μm, preferably 50 μm, more preferably 20 μm. 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.

[0133] When the nonaqueous electrolyte secondary battery is a nonaqueous electrolyte secondary battery containing a liquid nonaqueous electrolyte, the separator is composed of a separator. The separator can be appropriately selected from known separators. Examples of separators that can be used include a separator consisting of only a substrate layer, and a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. As the material for the substrate layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0134] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of non-aqueous electrolyte secondary batteries.

[0135] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0136] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0137] <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 an all-solid-state battery described above, for example, the manufacturing process 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 separator material (hereinafter also referred to as a separator solid electrolyte), (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) stacking the positive electrode, separator, and negative electrode, i.e., arranging the positive electrode mixture, negative electrode mixture, and separator solid electrolyte in layers so that the positive electrode mixture and negative electrode mixture sandwich the separator solid electrolyte, and stacking the layers together with a substrate.

[0138] (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.

[0139] (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.

[0140] (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.

[0141] (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.

[0142] In the case of a nonaqueous electrolyte secondary battery in which the nonaqueous electrolyte contains a nonaqueous electrolyte solution, a method for manufacturing a nonaqueous electrolyte secondary battery includes preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. The preparing of the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0143] The method for placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0144] <Electricity storage device> The energy storage element, nonaqueous electrolyte secondary battery, 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 plurality of energy storage elements, nonaqueous electrolyte secondary batteries, or all-solid-state secondary batteries 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, nonaqueous electrolyte secondary battery, or all-solid-state secondary battery included in the energy storage unit.

[0145] 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 element according to one embodiment of the present invention, a nonaqueous electrolyte secondary battery, and an all-solid-state secondary battery. 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.

[0146] <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.

[0147] 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 active material particles (a), positive electrode active material (b), positive electrode active material (c), electrode (a), and electrode (b) according to the present invention may be applied to a nonaqueous electrolyte energy storage element.

[0148] (Non-aqueous electrolyte) When the non-aqueous electrolyte is a liquid non-aqueous electrolytic solution, the non-aqueous electrolytic solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0149] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0150] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0151] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0152] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0153] The electrolyte salt can be appropriately selected from known electrolyte salts, and examples of the electrolyte salt include lithium salts.

[0154] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0155] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0156] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0157] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety. [Example]

[0158] 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.

[0159] [Example 1] (Preparation of coating agent) The coating agent was prepared as follows so that the coating layer formed would be a composite oxide represented by Li2TiO3. In an argon atmosphere glove box, titanium(IV) isopropoxide (Ti[(CH3)2CHO]4, Aldrich) and lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (manufactured by Aldrich) was added to prepare a coating agent. The amounts of titanium (IV) isopropoxide and lithium ethoxide solutions mixed were adjusted so that the molar ratio of titanium atoms to lithium atoms in the coating agent was 1:2.

[0160] (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, confirming that the coating layer on the active material particles thus obtained contained Li2TiO3 with a crystalline structure.

[0161] (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.

[0162] [Examples 2 to 5] The active material particles and energy storage elements of Examples 2 to 5 were prepared in the same manner as Example 1, except that the amount of coating agent applied was adjusted so that the content of the coating layer relative to the active material base material was as shown in Table 2.

[0163] [Comparative Example 1] The coating agent was prepared as follows so that the coating layer formed would be a composite oxide represented by Li2ZrO3. In an argon atmosphere glove box, a zirconium (IV) propoxide solution (Zr(OC3H7)4 in 1-propanol, Aldrich) and a lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (manufactured by Aldrich) was added to prepare a coating agent. The amounts of the zirconium (IV) propoxide solution and the lithium ethoxide solution mixed were adjusted so that the molar ratio of zirconium atoms to lithium atoms in the coating agent was 1:2. The active material particles and energy storage element of Comparative Example 1 were prepared in the same manner as in Example 1, except that the coating amount of the coating agent was adjusted using the above coating agent so that the content of the coating layer relative to the active material base material was as shown in Table 2.

[0164] Comparative Example 2 The coating agent was prepared as follows so that the coating layer formed would be a composite oxide represented by LiTaO3. In an argon atmosphere glove box, tantalum (V) ethoxide (Ta(OC2H5)5, Aldrich) and lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (manufactured by Aldrich) was added to prepare a coating agent. The amounts of tantalum (V) ethoxide and lithium ethoxide solutions mixed were adjusted so that the molar ratio of tantalum atoms to lithium atoms in the coating agent was 1:1. The active material particles and energy storage element of Comparative Example 2 were prepared in the same manner as in Example 1, except that the coating amount of the coating agent was adjusted using the above coating agent so that the content of the coating layer relative to the active material base material was as shown in Table 2.

[0165] [Comparative Examples 3 to 6] The coating layer formed is Li 4 / 3 Ti 5 / 3 The coating agent was prepared as follows to obtain a composite oxide represented by O4. In an argon atmosphere glove box, titanium(IV) isopropoxide (Ti[(CH3)2CHO]4, Aldrich) and lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (manufactured by Aldrich) was added to prepare a coating agent. The amounts of titanium (IV) isopropoxide and lithium ethoxide solutions mixed were adjusted so that the molar ratio of titanium atoms to lithium atoms in the coating agent was 5:4. The active material particles and energy storage elements of Comparative Examples 3 to 6 were prepared in the same manner as in Example 1, except that the amount of coating agent applied was adjusted so that the content of the coating layer relative to the active material base material was as shown in Table 2.

[0166] Comparative Example 7 LiNi, the positive electrode active material 1 / 2 Co1 / 5 Mn 3 / 10 An electricity storage element of Comparative Example 7 was produced in the same manner as in Example 1, except that O2 was not provided with a coating layer and was used as it was as active material particles.

[0167] <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. The discharge capacity in the first charge / discharge (0.1 C discharge capacity) and the ratio of the discharge capacity to the charge capacity in the first charge / discharge (charge / discharge efficiency) were determined. The results are shown in Table 2.

[0168] (2) Charge / discharge cycle test (1) Next, a charge-discharge cycle test (1) was carried out on each of the energy storage devices 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 2. Furthermore, for each of the energy storage elements after the capacity confirmation test (1) (before the charge-discharge cycle test (1)) and after the charge-discharge cycle test (1), the 1 kHz AC resistance was measured by AC impedance measurement at a temperature of 50°C and a state of charge (SOC) of 100%. The rate of increase in AC resistance after the charge-discharge cycle test (1) relative to the AC resistance after the capacity confirmation test (1) (before the charge-discharge cycle test (1)) was calculated as the resistance increase rate. The measurement results are shown in Table 2.

[0169] [Table 2]

[0170] As shown in Table 2, the resistance increase rate of each of the energy storage elements in Examples 1 to 5 was 130% or less, and the resistance increase accompanying the charge-discharge cycle was sufficiently suppressed. Furthermore, when comparing Examples 1 to 5, there is a tendency for the discharge capacity, charge-discharge efficiency, and capacity retention rate to increase by making the content of the coating layer relatively small relative to the content of the active material base material. On the other hand, the effect on the resistance increase rate was small even when the content of the coating layer was made relatively small, and the value was sufficiently low. In contrast, the coating layers in Comparative Examples 3 to 6 were Li 4 / 3 Ti 5 / 3 When O4 was used, the resistance increase rate was 230% or more, and the resistance increase due to charge / discharge cycles was not sufficiently suppressed. Furthermore, when the content of the coating layer was reduced, the resistance increase rate increased significantly. The effect of being able to sufficiently suppress the resistance increase even when the content of the coating layer was reduced is thought to be a unique effect that occurs when a specific composite oxide containing lithium atoms and titanium atoms is contained in the coating layer.

[0171] [Example 6] (Preparation of the solution to be attached to the base material) The composition ratio is Li2Ti 0.9 Nb 0.1 The solution to be attached to the base material was prepared as follows: Niobium (V) ethoxide (Nb(OCH2CH3)5, manufactured by Aldrich), titanium (IV) tetraisopropoxide (Ti[(CH3)2CHO)]4, manufactured by Aldrich), and lithium ethoxide solution (1.0 mol / dm) were added to ultra-dehydrated ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in an argon atmosphere glove box. 3C2H5OLi in ethanol (manufactured by Aldrich) was added to prepare a solution to be attached to the base material. The amounts of titanium (IV) tetraisopropoxide, niobium (V) ethoxide, and lithium ethoxide solutions were adjusted so that the molar ratio of niobium atoms, titanium atoms, and lithium atoms in the solution to be attached to the base material was 1:9:20.

[0172] (Preparation of particulate 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 attached 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 device's air inlet during coating was set to 140°C. The amount of solution to be attached to the base material was also adjusted so that the surface layer formed would be 0.20% by mass of the base material. Next, the base material, after drying to remove ethanol from the solution to be adhered to the surface of the base material particles, was heat-treated in an air atmosphere to form a surface layer, thereby obtaining positive electrode active material particles for a non-aqueous electrolyte secondary battery of Example 6. The heat treatment time was 30 minutes, and the heat treatment temperature was 400°C. Note that, hereinafter, "positive electrode active material particles for a non-aqueous electrolyte 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 Li2Ti 0.9 Nb 0.1 It is believed to be O3.

[0173] (Fabrication of non-aqueous electrolyte secondary battery) Using the obtained active material particles, a nonaqueous electrolyte secondary battery (all-solid-state secondary battery) of Example 6 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 was then removed from the ceramic powder compactor to obtain the nonaqueous electrolyte secondary battery (all-solid-state secondary battery) of Example 6.

[0174] [Examples 7 to 9] The active material particles and nonaqueous electrolyte secondary batteries of Examples 7 to 9 were produced in the same manner as in Example 6, except that the molar ratio of niobium atoms, titanium atoms, and lithium atoms in the solution to be adhered to the base material was adjusted so that the composition of the solution to be adhered to the base material was as shown in Table 3. The surface layer of each of the obtained active material particles was confirmed to be crystalline by the same method as in Example 6.

[0175] [Example 10] Active material particles and a nonaqueous electrolyte secondary battery of Example 10 were produced in the same manner as in Example 6, except that tantalum (V) ethoxide (Ta(OCH2CH3)5), manufactured by Aldrich) was used instead of niobium (V) ethoxide when preparing the solution to be attached to the base material. The surface layer of the obtained active material particles was confirmed to be crystalline by the same method as in Example 6.

[0176] [Examples 11 to 13] The active material particles and nonaqueous electrolyte secondary batteries of Examples 11 to 13 were produced in the same manner as in Example 8, except that the amount of solution to be attached to the base material was changed so that the ratio of the surface layer to the base material was as shown in Table 3. The surface layer of each of the obtained active material particles was confirmed to be crystalline by the same method as in Example 6.

[0177] [Comparative Example 8] Active material particles and a non-aqueous electrolyte secondary battery of Comparative Example 8 were produced in the same manner as in Example 6, except that no surface layer was formed on the base material.

[0178] Comparative Example 9 Active material particles and a nonaqueous electrolyte secondary battery of Comparative Example 9 were produced in the same manner as in Example 6, except that niobium (V) ethoxide was not used when preparing the solution to be attached to the base material, and the molar ratio of titanium atoms to lithium atoms in the solution to be attached to the base material was adjusted to 1:2. The surface layer of the obtained active material particles was confirmed to be crystalline by the same method as in Example 6.

[0179] [Example 14] (Preparation of the solution to be attached to the base material) The composition ratio is Li2Ti 0.9 Zr 0.1 The solution to be attached to the base material was prepared as follows: In an argon atmosphere glove box, ultra-dehydrated ethanol (Fujifilm Wako Pure Chemical Industries) was mixed with zirconium (IV) propoxide (Zr(OC3H7)4, Aldrich), titanium (IV) tetraisopropoxide (Ti[(CH3)2CHO)]4, Aldrich), and lithium ethoxide solution (1.0 mol / dm 3 C2H5OLi in ethanol (manufactured by Aldrich) was added to prepare a solution to be applied to the base material. The amounts of titanium (IV) tetraisopropoxide, zirconium (IV) propoxide, and lithium ethoxide solutions added were adjusted so that the molar ratio of zirconium atoms to titanium atoms to lithium atoms in the coating agent was 1:9:20.

[0180] (Preparation of particulate 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 attached 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 device's air inlet during coating was set to 140°C. The amount of solution to be attached to the base material was also adjusted so that the surface layer formed would be 0.20% by mass of the base material. Next, the ethanol was dried off from the solution to be adhered to the surface of the base material particles, and the base material in this state was heat-treated in an air atmosphere to form a surface layer, thereby obtaining positive electrode active material particles for a non-aqueous electrolyte secondary battery of Example 14. The heat treatment time was 30 minutes, and the heat treatment temperature was 400°C. Note that, hereinafter, "positive electrode active material particles for a non-aqueous electrolyte 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 Li2Ti 0.9 Zr 0.1 It is believed to be O3.

[0181] (Fabrication of non-aqueous electrolyte secondary battery) Using the obtained active material particles, a nonaqueous electrolyte secondary battery (all-solid-state secondary battery) of Example 14 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 was then removed from the ceramic powder compactor to obtain the nonaqueous electrolyte secondary battery (all-solid-state secondary battery) of Example 14.

[0182] [Examples 15 to 17] The active material particles and nonaqueous electrolyte secondary batteries of Examples 15 to 17 were produced in the same manner as in Example 14, except that the molar ratio of zirconium atoms, titanium atoms, and lithium atoms in the solution to be adhered to the base material was adjusted so that the composition of the solution to be adhered to the base material was as shown in Table 4. The surface layer of each of the obtained active material particles was confirmed to be crystalline by the same method as in Example 14.

[0183] [Examples 18 to 20] The active material particles and nonaqueous electrolyte secondary batteries of Examples 18 to 20 were produced in the same manner as in Example 16, except that the amount of solution to be attached to the base material was changed so that the ratio of the surface layer to the base material was as shown in Table 4. The surface layer of each of the obtained active material particles was confirmed to be crystalline by the same method as in Example 14.

[0184] [Comparative Example 10] Active material particles and a nonaqueous electrolyte secondary battery of Comparative Example 10 were produced in the same manner as in Example 14, except that no surface layer was formed on the base material.

[0185] [Comparative Example 11] Active material particles and a nonaqueous electrolyte secondary battery of Comparative Example 11 were produced in the same manner as in Example 14, except that zirconium (IV) propoxide was not used when preparing the solution to be attached to the base material, and the molar ratio of titanium atoms to lithium atoms in the solution to be attached to the base material was adjusted to 1:2. The surface layer of the obtained active material particles was confirmed to be crystalline by the same method as in Example 14.

[0186] <Rating 2> (1) Capacity confirmation test (2) For each of the obtained non-aqueous electrolyte secondary batteries, a capacity confirmation test (2) was carried out 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. 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 percentage of the discharge capacity at a discharge current of 1.0 C to the discharge capacity at a discharge current of 0.1 C was calculated, and the discharge capacity ratio at each rate was defined as 1 C / 0.1 C. The results are shown in Tables 3 and 4.

[0187] (2) Charge / discharge cycle test (2) For each of the nonaqueous electrolyte secondary batteries of Examples 6, 10, Comparative Examples 8 and 9, and Examples 14, 10 and 11, a charge-discharge cycle test (2) was carried out at 50° C. in the following manner. Constant current and constant voltage charging was performed with a charging current of 0.2C and a charging cut-off voltage of 3.75V. The end condition of charging was until the charging current reached 0.05C. Thereafter, constant current discharging was performed with a discharging current of 0.2C and a discharging cut-off voltage of 2.25V. After charging and discharging, a rest time of 10 minutes was provided respectively. This charge-discharge cycle was carried out 50 times. The discharge capacity of the 50th cycle was divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate after 50 cycles. The results are shown in Table 3 and Table 4. Also, for each non-aqueous electrolyte secondary battery of Example 6, Example 10, Comparative Example 8 and Comparative Example 9, and Example 14, Comparative Example 10 and Comparative Example 11 after the above capacity confirmation test (2) (before the charge-discharge cycle test (2)) and after the above charge-discharge cycle test (2), the AC resistance at a frequency of 1 kHz at SOC (State of Charge) 100% was measured at 50°C. The increase rate of the AC resistance after the charge-discharge cycle test (2) with respect to the AC resistance after the capacity confirmation test (2) was obtained by the following formula (1) and taken as the resistance increase rate. The results are shown in Table 3 and Table 4. Resistance increase rate = [((AC resistance after charge-discharge cycle test (2)) - (AC resistance after capacity confirmation test (2))) / (AC resistance after capacity confirmation test (2))] × 100 ···(1)

[0188]

Table 3

[0189]

Table 4

[0190] As shown in Table 3, on the surface of the base material composed of a material capable of occluding and releasing lithium ions, at least one element (A 2 element) including each element of lithium, titanium, oxygen, and a monatomic cation of pentavalent or higher, and when the molar ratio of the titanium to the A 2 element is Ti:A 2 [[ID=2 A nonaqueous electrolyte secondary battery was obtained in which the decrease in battery capacity during high-rate discharge was suppressed compared to Comparative Example 9, which did not contain any element. Some of the positive electrode active materials of the Examples resulted in nonaqueous electrolyte secondary batteries in which the decrease in battery capacity during high-rate discharge was suppressed compared to Comparative Example 8, which did not have a surface layer. Furthermore, a comparison of Examples 6 and 10 with Comparative Example 8 shows that the positive electrode active material having the above-mentioned surface layer resulted in nonaqueous electrolyte secondary batteries in which the decrease in battery capacity due to repeated charge and discharge was suppressed.

[0191] As shown in Table 4, the surface of a base material made of a substance capable of absorbing and releasing lithium ions is coated with lithium, titanium, oxygen, and at least one element (A) that becomes a tetravalent monoatomic cation having an ionic radius of more than 0.0605 nm when the coordination number is 6. 3 The positive electrode active material of the embodiment has a surface layer containing each of the elements A 3 A nonaqueous electrolyte secondary battery was obtained in which the decrease in battery capacity during high-rate discharge was suppressed compared to Comparative Example 11, which did not contain any element. Some of the positive electrode active materials of the Examples resulted in nonaqueous electrolyte secondary batteries in which the decrease in battery capacity during high-rate discharge was suppressed compared to Comparative Example 10, which did not have a surface layer. Furthermore, a comparison between Example 14 and Comparative Example 10 shows that the positive electrode active material having the above-mentioned surface layer resulted in a nonaqueous electrolyte secondary battery in which the decrease in battery capacity due to repeated charge and discharge was suppressed. [Industrial Applicability]

[0192] 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]

[0193] 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 Energy storage device

Claims

1. A base material composed of a material capable of absorbing and releasing lithium ions; and present on the surface of the base material, Lithium, titanium, oxygen, and at least one element that becomes a monatomic cation with a valence of five or more (A ２ element), and The titanium and the A ２ The mole ratio of the element is Ti:A ２ = (1-x ２ ): x ２ When 0<x ２ Satisfying ≦0.5 surface layer A positive electrode active material for a non-aqueous electrolyte secondary battery comprising:

2. The surface layer has the composition formula Li ａ２ (Ti １－ｘ２ A ２ ｘ２ ) ｂ２ O ｃ２ (However, A ２ is at least one element that forms a monatomic cation with a valence of five or more; ２ , b ２ , c ２ are respectively 1<a ２ <4, 1≦b ２ <2, 2<c ２ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein R is a real number satisfying 0.05<4.

0.

3. A base material composed of a material capable of absorbing and releasing lithium ions; and present on the surface of the base material, and Lithium, titanium, oxygen, and at least one element that forms a tetravalent monoatomic cation having an ionic radius of more than 0.0605 nm when the coordination number is 6 (A ３ Contains each element of surface layer A positive electrode active material for a non-aqueous electrolyte secondary battery comprising:

4. The surface layer has the composition formula Li ａ３ (Ti １－ｘ３ A ３ ｘ３ ) ｂ３ O ｃ３ (However, A ３ is at least one element that forms a tetravalent monoatomic cation having an ionic radius of more than 0.0605 nm when the coordination number is 6; ３ , b ３ , c ３ , x ３ are respectively 1<a ３ <4, 1≦b ３ <2, 2<c ３ <4, 0<x ３ The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3 , wherein R 1 is a real number satisfying 1.

5. An electrode comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 and a solid electrolyte.

6. An electrode for a non-aqueous electrolyte secondary battery, comprising a positive electrode active material layer containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 .

7. An electric storage element comprising the electrode according to claim 5 or 6.

8. A non-aqueous electrolyte secondary battery comprising the electrode according to claim 5 or 6.

9. An all-solid-state secondary battery comprising the electrode according to claim 5 or 6 and a solid electrolyte.

10. An electricity storage device comprising two or more electricity storage elements, and comprising at least one of the electricity storage element according to claim 7, the nonaqueous electrolyte secondary battery according to claim 8, and the all-solid-state secondary battery according to claim 9.

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