Aggregates, sheets, separators, electrodes, and energy storage devices

Abstract

The present invention provides: aggregates wherein dendrite growth of Li metal can be reduced; a sheet; a separator; an electrode; and a power storage device. Aggregates (10) each comprise oxide particles (19) that have a garnet crystal structure containing Li, La and Zr, and inorganic particles (22) that are formed of a typical element and contain Mg. The median diameter of the inorganic particles is 1 / 2 or less of the median diameter of the oxide particles, and the ratio of the inorganic particles to the oxide particles is 1 vol% to 10 vol%. A power storage device (11) comprises the aggregates.

Description

[Technical Field]

[0001] The present invention relates to aggregates, sheets, separators, electrodes, and energy storage devices containing oxide particles having a garnet-type crystal structure. [Background technology]

[0002] Patent Document 1 discloses an oxide having a garnet-type crystal structure containing Li, La, and Zr, which includes Li, La, and Zr, and at least one of Mg and A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba). This type of oxide is known to be stable with respect to Li metal and is expected to be used as a solid electrolyte material for energy storage devices. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-40767 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] When a battery storage device is charged, a phenomenon can occur where dendrites (dendritic crystals) of lithium metal grow from the negative electrode towards the positive electrode. If these lithium metal dendrites come into contact with the positive electrode, a short circuit occurs. Short circuits are particularly likely to occur when oxide particles are used as the material, as dendrites grow along the grain boundaries.

[0005] This invention was made to solve this problem and aims to provide an aggregate and energy storage device that can reduce the growth of Li metal dendrites. [Means for solving the problem]

[0006] A first embodiment for achieving this objective is an aggregate comprising oxide particles having a garnet-type crystalline structure containing Li, La, and Zr, and inorganic particles consisting of typical elements and containing Mg. The median diameter of the inorganic particles is 1 / 2 or less of the median diameter of the oxide particles, and the ratio of inorganic particles to oxide particles is 1 vol% or more and 10 vol% or less.

[0007] A second embodiment is the first embodiment, further comprising an electrolyte.

[0008] The third aspect is a sheet, which includes the aggregate in the first or second aspect.

[0009] A fourth aspect is an electrode comprising the aggregate in the first or second aspect, or the electrode is in contact with a protective layer comprising the aggregate in the first or second aspect.

[0010] A fifth aspect is a separator comprising the aggregate in the first or second aspect, or the separator is in contact with a protective layer comprising the aggregate in the first or second aspect.

[0011] The sixth embodiment is an energy storage device, which includes the electrodes of the fourth embodiment, or the energy storage device includes the separator of the fifth embodiment. [Effects of the Invention]

[0012] According to the aggregate of the present invention, inorganic particles consisting of typical elements and containing Mg are present between oxide particles. Since the inorganic particles consisting of typical elements and containing Mg are insulators, the presence of inorganic particles between oxide particles can reduce dendrite growth of Li metal at grain boundaries. According to the sheet, separator, electrode, or energy storage device of the present invention, dendrite growth can be reduced because it contains the aggregate. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of an energy storage device including an aggregate in the first embodiment. [Figure 2]This is a cross-sectional view of the aggregate, enlarged from the portion shown in section II of Figure 1. [Figure 3] This is a schematic diagram showing the crystal structure of a garnet-type crystal. [Figure 4] This is a cross-sectional view of the energy storage device in the second embodiment. [Figure 5] This is a cross-sectional view of the energy storage device in the third embodiment. [Figure 6] (a) is a cross-sectional view of the insulator in the fourth embodiment, (b) is a cross-sectional view of the electrode in the fifth embodiment, and (c) is a cross-sectional view of the electrode in the sixth embodiment. [Modes for carrying out the invention]

[0014] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a schematic cross-sectional view of an energy storage device 11 including the assembly 10 in the first embodiment. The energy storage device 11 is a primary or secondary battery using lithium as a carrier ion. The energy storage device 11 in this embodiment is a lithium-ion solid-state battery (secondary battery) in which the power generation element is composed of solid material. The statement that the power generation element is composed of solid material means that the framework of the power generation element is composed of solid material, and includes a form in which liquid is impregnated into the framework.

[0015] The energy storage device 11 includes, in order, a positive electrode layer 12, an electrolyte layer 15, and a negative electrode layer 16. The positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 are all sheets. The positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 are housed in a case (not shown). The electrolyte layer 15 consists of an aggregate 10. The aggregate 10 contains oxide particles 19. In this embodiment, the electrolyte layer 15 corresponds to a separator. The separator isolates the positive electrode layer 12 and the negative electrode layer 16, electrically insulating them from each other.

[0016] The positive electrode layer 12 consists of a current collector layer 13 and an active material layer 14 superimposed on each other. The current collector layer 13 is a conductive material. Examples of materials for the current collector layer 13 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0017] The active material layer 14 includes the polymer 10 and the active material 20. In order to reduce the resistance of the active material layer 14, a conductive assistant may be included in the active material layer 14. Examples of the conductive assistant include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0018] Examples of the active material 20 include metal oxides having transition metals, sulfur-based active materials, and organic-based active materials. Examples of the metal oxides having transition metals include metal oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V and Li. Examples of the metal oxides having transition metals include LiCoO2, LiNi , , ,

[0020] , 12 ,

[0021] , , ,

[0019] Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, and LiFePO4 are exemplified.

[0019] For the purpose of suppressing the reaction between the active material 20 and the oxide particles 19, a coating layer can be provided on the surface of the active material 20. Examples of the coating layer include Al2O3, ZrO2, LiNbO3, Li4Ti5O 12 , LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, and Li2MoO4 are exemplified.

[0020] Examples of the sulfur-based active materials include S, TiS2, NiS, FeS2, Li2S, MoS3, and sulfur-carbon composites. Examples of the organic-based active materials include radical compounds typified by 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radicalene compounds, tetracyanoquinodimethane, and phenazine oxide.

[0021] The negative electrode layer 16 is formed by laminating a current collector layer 17 and an active material layer 18. The current collector layer 17 is a conductive member. Examples of the material of the current collector layer 17 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0022] The active material layer 18 contains a polymer 10 and an active material 21. In order to reduce the resistance of the active material layer 18, a conductive additive may be contained in the active material layer 18. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. The active material 21 includes Li, Li-Al alloy, Li4Ti5O 12 , graphite, In, Si, Si-Li alloy, and SiOx (for example, 0.5 < X < 1.5). The polymer 10 has a great effect when the active material 21 contains Li metal.

[0023] FIG. 2 is a cross-sectional view of the polymer 10. FIG. 2 schematically shows an enlarged view of the portion indicated by II in FIG. 1. The polymer 10 includes oxide particles 19, inorganic particles 22, and an electrolytic solution 23. The oxide particles 19 are composed of a composite oxide having a garnet-type crystal structure containing Li, La, and Zr. The garnet-type crystal structure is represented by the general formula C3A2B3O 12 as represented.

[0024] FIG. 3 is a diagram schematically showing the garnet-type crystal structure. In the garnet-type crystal structure, Sc at the C site is coordinated with 12 oxygen atoms Oa in an icosahedral coordination, Sa at the A site is coordinated with 8 oxygen atoms Oa in an octahedral coordination, and Sb at the B site is coordinated with 4 oxygen atoms Oa in a tetrahedral coordination. In the oxide particles 19, at a position where it is coordinated with 8 oxygen atoms Oa in a normal garnet-type crystal structure and becomes a void V, Li may be present. The void V is, for example, a position sandwiched between B site Sb1 and B site Sb2. Li present in the void V is octahedrally coordinated with oxygen atoms Oa constituting an octahedron including a tetrahedral face Fb1 forming B site Sb1 and a tetrahedral face Fb2 forming B site Sb2. For example, Li7La3Zr2O having a garnet-type crystal structure 12In this case, La may occupy site C (Sc), Zr may occupy site A (Sa), and Li may occupy site B (Sb) and the void V.

[0025] Garnet-type crystal structures can be identified by X-ray diffraction. The garnet-type crystal structure is found in the Cambridge Structural Database (CSD) X-ray diffraction file No. 422259 (Li7La3Zr2O 12 It has an XRD pattern similar to ).Oxide particle 19 may differ from No. 422259 in terms of constituent elements and Li concentration, so the diffraction angle and intensity ratio may differ.A typical crystal structure of this type is cubic (space group Ia-3d (- indicates an overline meaning reversal operation), JCPDS:84-1753).

[0026] Let's return to Figure 2 for explanation. Oxide particles 19 are typically Li7La3Zr2O 12 For example, the oxide particle 19 is Li7La3Zr2O 12 Some of the constituent elements may be substituted with other elements, or trace amounts of other elements may be added without substituting any constituent elements. Examples of other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0027] The oxide particles 19 are, for example, Li6La3Zr 1.5 W 0.5 O 12 Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 Li 6.25 La3Zr2Ga 0.25 O 12 Li 6.4 La3Zr 1.4 Ta 0.6 O12 Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 Li 6.20 Ba 0.30 La 2.95 Rb 0.05 Zr2O 12 These are some examples.

[0028] The oxide particles 19 preferably contain at least one of Mg and element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba), and the molar ratio of each element satisfies all of (1) to (3) below, or contain both Mg and element A, and the molar ratio of each element satisfies all of (4) to (6) below. Element A is preferably Sr in order to increase the ionic conductivity of the oxide particles 19. (1) 1.33 ≤ Li / (La+A) ≤ 3 (2) 0 ≤ Mg / (La+A) ≤ 0.5 (3) 0 ≤ A / (La + A) ≤ 0.67 (4) 2.0 ≤ Li / (La+A) ≤ 2.6 (5) 0.01 ≤ Mg / (La+A) ≤ 0.14 (6) 0.04 ≤ A / (La + A) ≤ 0.17

[0029] The inorganic particles 22 are composed of typical elements and contain Mg. Typical elements are elements of groups 1, 2, and 12-18 of the periodic table according to the IUPAC 1990 recommendations. Examples of materials for the inorganic particles 22 include MgO, Mg2SiO4, Mg2Si2O6, Mg2Si3O8, MgAl2O4, Mg2Si, Mg3(PO4)2, MgN2, MgB2, MgF2, MgI2, Li-Mg-O, Li-Mg-Al-O, etc. Since the inorganic particles 22, composed of typical elements and containing Mg, are insulators, even if the oxide particles 19 in contact with the highly reducing Li metal become electrically conductive, the presence of inorganic particles 22 between the oxide particles 19 reduces the growth of Li dendrites at the interface of the oxide particles 19. This reduces the occurrence of short circuits in the electrolyte layer 15.

[0030] In the aggregate 10, the ratio of inorganic particles 22 to oxide particles 19 is preferably 1% by volume or more and 10% by volume or less. This is to reduce the dendrite growth of Li metal by the presence of inorganic particles 22, while preventing the resistance of the energy storage device 11 containing the inorganic particles 22 from becoming excessively high.

[0031] The proportion of inorganic particles 22 is first determined by analyzing the cross-section of the active material layer 14, 18 or electrolyte layer 15 (polished surface, surface obtained by irradiation with a focused ion beam (FIB), or surface obtained by ion milling) using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) to identify oxide particles 19 and inorganic particles 22. The polished surface is, for example, a surface obtained by freezing the active material layer 14, 18 or electrolyte layer 15, or by embedding and solidifying the active material layer 14, 18 or electrolyte layer 15 in a tetrafunctional epoxy resin, and then polishing it. The analysis involves identifying the distribution of La, Zr, and Mg in the cross-section and performing image analysis of the contrast of the backscattered electron image to determine the area of ​​oxide particles 19 and inorganic particles 22. The proportion of inorganic particles 22 (volume %) is obtained by considering the ratio of the area of ​​inorganic particles 22 to the area of ​​oxide particles 19 as the volume ratio.

[0032] The median diameter of the inorganic particles 22 is preferably smaller than the median diameter of the oxide particles 19. This is because the inorganic particles 22 are positioned in the gaps between the oxide particles 19 where Li metal dendrites grow and on the surface of the oxide particles 19. In particular, the median diameter of the inorganic particles 22 is 1 / 2 or less of the median diameter of the oxide particles 19, and more preferably 1 / 5 or less of the median diameter of the oxide particles 19.

[0033] To determine the median diameter of oxide particles 19 and inorganic particles 22, first, SEM images of the oxide particles 19 and inorganic particles 22 appearing in the cross-section of the active material layer 14, 18 or electrolyte layer 15 are analyzed. The equivalent circular diameter is calculated from the area of ​​each particle of oxide particles 19 and inorganic particles 22, and the volume-based particle size distribution is determined. The median diameter is the equivalent circular diameter at which the cumulative value of the frequencies in the particle size distribution reaches 50%. To ensure accuracy, the image used to determine the particle size distribution is 400 μm of the cross-section. 2 The area shall be as stated above.

[0034] When the oxide particles 19 and inorganic particles 22 are in a flowing state (powder state before tape molding or pressure molding), the median diameter of the oxide particles 19 and inorganic particles 22 can be determined by particle size distribution measurement using laser diffraction and scattering.

[0035] The electrolyte 23 is a solution in which a lithium salt is dissolved in a solvent. The solvent is not particularly limited as long as it can dissolve the lithium salt. Examples of solvents include carbonate esters, aliphatic carboxylic acid esters, phosphate esters, γ-lactones, ethers, nitriles, sulfolanes, dimethyl sulfoxides, fluorescein solvents, and ionic liquids. Mixtures of these may also be used.

[0036] Examples of carbonate esters include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, as well as linear carbonate esters such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

[0037] Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of γ-lactones include γ-butyrolactone. Examples of ethers include linear ethers such as 1,2-dialkoxyethane and cyclic ethers such as 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of nitriles include acetonitrile and propionitrile. Fluorine solvents are compounds in which hydrogen atoms of hydrocarbons are replaced with fluorine atoms and their derivatives.

[0038] Ionic liquids are compounds composed of cations and anions, and are liquids at room temperature and pressure. If the solvent of the electrolyte is an ionic liquid, the flame retardancy of the electrolyte can be improved. Preferably, the ionic liquid contains one or more cation species selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0039] The anionic component of the ionic liquid is not particularly limited. The anionic component is BF4 - ,N(SO2F)2 - Inorganic anions such as B(C6H5)4 - CH3SO3 - CF3SO3 - ,N(SO2CF3)2 - ,N(SO2C4F9)2 - Examples of organic anions include N(SO2F)2. - [FSI] is an abbreviation for [FSI] - : Called bis(fluorosulfonyl)imide anion, N(SO2CF3)2 - [TFSI] is an abbreviation for [TFSI] - It is sometimes called bis(trifluoromethanesulfonyl)imide anion.

[0040] Ionic liquids include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME-FSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), N-butyl-N-methylpiperidinium bis(fluorosulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13-FSI), and N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13-TFSI). Mixtures of these may also be used.

[0041] The ionic liquid may be a solvated ionic liquid. Examples of solvated ionic liquids include those obtained by dissolving a lithium salt in a sulfone solvent such as sulfolane or a sulfolane derivative, or a glyme solvent such as tetraglyme.

[0042] The lithium salt is a compound used for the transfer of cations between the positive electrode layer 12 and the negative electrode layer 16. The anion of the lithium salt is a halide ion (I - , Cl - , Br - , etc.), SCN - , BF4 - , BF3(CF3) - , BF3(C2F5) - , PF6 - , ClO4 - , SbF6 - , N(SO2F)2 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , B(C6H5)4 - , B(O2C2H4)2 - , C(SO2F)3 -,C(SO2CF3)3 - CF3COO - CF3SO2O - ,C6F5SO2O - ,B(O2C2O2)2 - RCOO - Examples include (where R is an alkyl group having 1-4 carbon atoms, a phenyl group, or a naphthyl group). The lithium salt may also be a mixture of these.

[0043] In the aggregate 10, the volume of oxide particles 19 accounts for 52% or more and less than 100% of the total volume of oxide particles 19 and electrolyte 23, preferably 61% or more and less than 100%. The combination of oxide particles 19 and electrolyte 23 reduces the interfacial resistance of the oxide particles 19, allowing the ion transport rate of the aggregate 10 to be greater than that of a typical electrolyte. As a result, the operational stability of the energy storage device 11 in which the aggregate 10 is placed is increased.

[0044] The content (volume %) of oxide particles 19 is determined by analyzing a randomly selected 5000x magnification field of view from the cross-section of the active material layer 14, 18, or electrolyte layer 15 using an EDS-equipped SEM. The analysis identifies the area of ​​oxide particles 19 and the area of ​​electrolyte 23 by identifying the distribution of La and Zr and performing image analysis of the contrast of the backscattered electron image. The content (volume %) of oxide particles 19 is obtained by considering the ratio of the area of ​​oxide particles 19 to the total area of ​​oxide particles 19 and electrolyte 23 as the volume ratio.

[0045] The lithium salt concentration in electrolyte 23 is 0.2 mol / dm³ 3 The above is preferable, and preferably 0.5 mol / dm 3 That concludes the explanation. As the salt concentration increases, the number of solvent molecules coordinating to the carrier ions increases and the number of uncoordinated solvents decreases, thus reducing the interfacial resistance of the oxide particles 19. The salt concentration of the electrolyte 23 is 4.0 mol / dm³ 3 The following is preferable: The salt concentration of electrolyte 23 is 4.0 mol / dm³ 3 This is because, beyond a certain point, the ionic conductivity tends to decrease significantly due to the increased viscosity of the electrolyte 23.

[0046] The aggregate 10 may contain a binder that binds the oxide particles 19. Examples of binders include rubbery polymers such as fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene / hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0047] Examples of vinylidene fluoride polymers include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and copolymerizable monomers. Examples of copolymerizable monomers include halogen-containing monomers (excluding vinylidene fluoride) and non-halogen-containing copolymerizable monomers. Examples of halogen-containing monomers include chlorine-containing monomers such as vinyl chloride; and fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ethers. Examples of non-halogen-containing copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, their esters or salts; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers polymerize with vinylidene fluoride to form a copolymer.

[0048] The energy storage device 11 is manufactured, for example, as follows: After compounding an electrolyte 23 with a mixture of oxide particles 19 and inorganic particles 22, a solution of a binder dissolved in a solvent is mixed in to make a slurry. After forming the slurry into a sheet, it is dried to obtain a green sheet (electrolyte sheet) for the electrolyte layer 15.

[0049] After compounding the mixture of oxide particles 19 and inorganic particles 22 with the electrolyte 23, the active material 20 is mixed in, and then a solution of the binder dissolved in the solvent is added to make a slurry. After coating the current collector layer 13 with the slurry, it is dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 12.

[0050] After compounding an electrolyte 23 with a mixture of oxide particles 19 and inorganic particles 22, the active material 21 is mixed in, and then a solution of binder dissolved in a solvent is added to create a slurry. After coating the current collector layer 17 with the slurry, it is dried to obtain a green sheet (negative electrode sheet) for the negative electrode layer 16.

[0051] After cutting the electrolyte sheet, positive electrode sheet, and negative electrode sheet into predetermined shapes, they are stacked in the order of positive electrode sheet, electrolyte sheet, and negative electrode sheet, and then pressed together to form a single unit. Terminals (not shown) are connected to the current collector layers 13 and 17, respectively, and the unit is sealed in a case (not shown) to obtain an energy storage device 11 including a positive electrode layer 12, an electrolyte layer 15, and a negative electrode layer 16.

[0052] A second embodiment will be described with reference to Figure 4. In the first embodiment, the case in which the assembly 10 is used in a primary or secondary battery in which the power generation element is composed of solids was described. In the second embodiment, the case in which the assembly 10 is used in a liquid lithium-ion battery that uses an organic solvent as the electrolyte will be described. Parts that are the same as those described in the first embodiment are denoted by the same reference numerals and their descriptions are omitted below. Figure 4 is a cross-sectional view of the energy storage device 24 in the second embodiment.

[0053] The energy storage device 24 includes, in order, a positive electrode layer 12, a separator 25, and a negative electrode layer 16. These are housed in a case (not shown). The separator 25 is made of a porous material that is durable against the active materials 20, 21 and electrolyte contained in the positive electrode layer 12 and the negative electrode layer 16, and allows lithium ions to pass through but does not conduct electricity. Examples of separators 25 include nonwoven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc. The electrolyte is the same as that described in the first embodiment, so its description is omitted.

[0054] In the second embodiment, the energy storage device 24 includes aggregates 10 in the positive electrode layer 12 and the negative electrode layer 16, so dendrite growth can be reduced in the same way as in the energy storage device 11 in the first embodiment.

[0055] A third embodiment will be described with reference to Figure 5. In the first and second embodiments, cases in which the aggregate 10 is included in the positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 were described. In the third embodiment, a case in which the aggregate 10 is included in the protective layers 29 and 32 will be described. Parts identical to those described in the first and second embodiments are denoted by the same reference numerals and their descriptions are omitted below. Figure 5 is a cross-sectional view of the energy storage device 26 in the third embodiment.

[0056] The energy storage device 26 includes, in order, a positive electrode layer 27, a separator 25, and a negative electrode layer 30. These are housed in a case (not shown). The energy storage device 26 is a liquid lithium-ion battery that uses an organic solvent as the electrolyte.

[0057] The positive electrode layer 27 consists of a current collector layer 13 and an active material layer 28 superimposed on each other. The active material layer 28 contains an active material 20. To lower the resistance of the active material layer 28, the active material layer 28 may contain conductive additives such as carbon black, acetylene black, Ketjenblack, carbon fiber, Ni, Pt, and Ag.

[0058] A protective layer 29 is placed between the separator 25 and the negative electrode layer 30. The protective layer 29 includes an aggregate 10.

[0059] The negative electrode layer 30 consists of an active material layer 31, a protective layer 32, and a current collector layer 17 stacked in that order. The active material layer 31 is made of, for example, Li, Li-Al alloy, Li-Sn alloy, Li-Si alloy, Li-Mg alloy, Li-Si alloy, or Si-Li alloy. The protective layer 32 contains aggregates 10. The protective layers 29 and 32 are arranged by laminating sheets of slurry containing aggregates 10, or by applying slurry containing aggregates 10 to the separator 25 and the current collector layer 17.

[0060] The oxide particles 19, which have a garnet-type crystalline structure containing Li, La, and Zr and are contained in the aggregate 10, are resistant to reduction of metallic lithium in the active material layer 31, thereby increasing the operational stability of the energy storage device 26. Furthermore, the protective layer 29 interposed between the active material layer 31 and the separator 25 suppresses short circuits caused by dendrite growth of metallic lithium. The protective layer 32 interposed between the active material layer 31 and the current collector layer 17 suppresses deterioration of the current collector layer 17.

[0061] The fourth to sixth embodiments will be described with reference to Figure 6. Parts identical to those described in the first to third embodiments will be denoted by the same reference numerals, and their subsequent descriptions will be omitted. Figure 6(a) is a cross-sectional view of the insulator 33 in the fourth embodiment.

[0062] The insulator 33 comprises a separator 25 and a protective layer 29 in contact with the separator 25. The separator 25 includes a first interface 34 and a second interface 35 opposite to the first interface 34, and the protective layer 29 is disposed at both the first interface 34 and the second interface 35. The protective layer 29 disposed at the separator 25 reduces short circuits caused by dendrite growth of metallic lithium contained in the energy storage device. Even if a short circuit occurs in the energy storage device and the separator 25 attempts to deform due to heat, the protective layer 29 maintains the shape of the separator 25 and suppresses thermal runaway of the energy storage device.

[0063] Figure 6(b) is a cross-sectional view of the electrode 36 in the fifth embodiment. The electrode 36 comprises a positive electrode layer 12 and a protective layer 29 in contact with the active material layer 14 of the positive electrode layer 12. The protective layer 29 is positioned at the interface 37 of the electrode 36 opposite to the surface of the active material layer 14 on which the current collecting layer 13 is located. The protective layer 29 positioned at the interface 37 of the active material layer 14 can reduce dendrite growth from the negative electrode layer 16 of the energy storage device.

[0064] Figure 6(c) is a cross-sectional view of the electrode 38 in the sixth embodiment. The electrode 38 comprises a negative electrode layer 16 and a protective layer 29 in contact with the active material layer 18 of the negative electrode layer 16. The protective layer 29 of the electrode 38 is positioned at the interface 39 opposite to the surface of the active material layer 18 on which the current collecting layer 17 is located. The protective layer 29 positioned at the interface 39 of the active material layer 18 can reduce dendrite growth from the negative electrode layer 16 of the energy storage device.

[0065] The insulator 33 is placed in the energy storage device in place of the separator 25 of the energy storage device 24 in the second embodiment or the energy storage device 26 in the third embodiment. The insulator 33 may omit one of the two protective layers 29 placed at the interfaces 34, 35 of the separator 25.

[0066] Electrode 36 is placed in the energy storage device in place of the positive electrode layers 12 and 27 of the energy storage device 24 in the second embodiment and the energy storage device 26 in the third embodiment. Electrode 38 is placed in the energy storage device in place of the negative electrode layers 16 and 30 of the energy storage device 24 in the second embodiment and the energy storage device 26 in the third embodiment. [Examples]

[0067] The present invention will be described in more detail by reference to examples, but the present invention is not limited to these examples.

[0068] (Preparation of the first oxide particles) Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed accordingly. Li2CO3 was kept in excess by approximately 15 mol% in elemental terms, considering the volatilization of Li during calcination. The weighed raw materials and organic solvents were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. After drying the slurry removed from the pot, it was placed on an MgO plate and calcined at 900°C for 1 hour and then at 1200°C for 10 hours. The calcined powder was placed on an MgO plate and calcined at 1100°C for 4 hours in an inert gas atmosphere. The calcined powder was wet-milled in a planetary ball mill in an air-free environment and then dried to obtain the first oxide particles. The median diameter of the first oxide particles, determined by particle size distribution measurement using laser diffraction and scattering, was 3.2 μm.

[0069] (Preparation of the second oxide particle) Li 6.65 La3Zr 1.65 Ta 0.35 O 12 Li2CO3, La(OH)3, ZrO2, and Ta2O5 were weighed accordingly. Li2CO3 was kept in excess by approximately 15 mol% in elemental terms, considering the volatilization of Li during calcination. The weighed raw materials and organic solvent were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. After drying the slurry removed from the pot, it was placed on an Al2O3 plate and calcined at 900°C for 1 hour and then at 1200°C for 10 hours. The calcined powder was placed on an Al2O3 plate and calcined at 1100°C for 4 hours in an inert gas atmosphere. The calcined powder was wet-milled in a planetary ball mill in an air-free environment and then dried to obtain the second oxide particles. The median diameter of the second oxide particles, determined by particle size distribution measurement using laser diffraction and scattering, was 3.1 μm.

[0070] (Preparation of electrolyte solution) The lithium salt LiN(SO2F)2(LiFSI) was dissolved in the ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) to a salt concentration of 2.1 mol / dm³. 3 We obtained the electrolyte.

[0071] (Example 1) A mixed powder (3 vol%) of inorganic particles was obtained by mixing the first oxide particles with inorganic particles MgO. Then, the electrolyte was added to the mixed powder in a ratio of mixed powder:electrolyte = 61:39 (vol%), and the mixture was mixed in a mortar to obtain the aggregate in Example 1. The median diameter of the inorganic particles, determined by particle size distribution measurement using laser diffraction and scattering, was 0.54 μm.

[0072] (Example 2) The electrolyte was added to the first oxide particles in a ratio of oxide particles:electrolyte = 61:39 (vol%), and the mixture was mixed in a mortar to obtain the aggregate shown in Example 2. Analysis of the first oxide particles by SEM-EDS and time-of-flight secondary ion mass spectrometry (TOF-SIMS) revealed the presence of Li-Mg-O particles (inorganic particles) on the surface of the oxide particles. These inorganic particles are presumed to have been generated during the preparation of the first oxide particles.

[0073] (Example 3) A mixed powder was obtained by mixing inorganic MgO particles with the second oxide particles (the ratio of inorganic particles to oxide particles was 3 vol%). Then, the electrolyte was added to the mixed powder in a ratio of mixed powder:electrolyte = 61:39 (vol%), and the mixture was mortared to obtain the aggregate in Example 3. The median diameter of the inorganic particles, determined by particle size distribution measurement using laser diffraction and scattering, was 0.54 μm.

[0074] (Example 4) The aggregate in Example 4 was obtained in the same manner as in Example 1, except that the median diameter of the inorganic particles was set to 1.0 μm.

[0075] (Example 5) The aggregate in Example 5 was obtained in the same manner as in Example 1, except that the median diameter of the inorganic particles was set to 1.5 μm.

[0076] (Example 6) The aggregate in Example 6 was obtained in the same manner as in Example 1, except that the ratio of inorganic particles MgO to the first oxide particles was 1 vol%.

[0077] (Example 7) The aggregate in Example 7 was obtained in the same manner as in Example 1, except that the ratio of inorganic MgO particles to the first oxide particles was set to 5 vol%.

[0078] (Example 8) The aggregate in Example 8 was obtained in the same manner as in Example 1, except that the ratio of inorganic MgO particles to the first oxide particles was set to 10 vol%.

[0079] (Comparative Example 1) The electrolyte was added to the second oxide particles in a ratio of oxide particles:electrolyte = 61:39 (vol%), and mixed in a mortar to obtain the aggregate shown in Comparative Example 1.

[0080] (Comparative Example 2) The aggregate in Comparative Example 2 was obtained in the same manner as in Example 1, except that the ratio of inorganic particles MgO to the first oxide particles was 15 vol%.

[0081] (Comparative Example 3) The aggregate for Comparative Example 3 was obtained in the same manner as in Example 1, except that the median diameter of the inorganic particles was set to 3.0 μm.

[0082] (Creating symmetrical cells) In an Ar atmosphere, the aggregates from Example 1-8 and Comparative Example 1-3 were placed into a cylindrical insulating member with an inner diameter of 10 mm, respectively, and molded bodies from Example 1-8 and Comparative Example 1-3 were obtained by uniaxial pressurization (pressure 360 ​​MPa). Li metal foil with a diameter of 10 mm was adhered to both sides of the molded body to obtain symmetrical cells from Example 1-8 and Comparative Example 1-3.

[0083] (Test method) In the symmetrical cells of Examples 1-8 and Comparative Examples 1-3, a constant DC current was passed between the metal foils on both sides for 500 seconds. If a short circuit did not occur, the current density was slightly increased and a constant DC current was passed again. This process was repeated until a short circuit occurred, and the current density at the time of the short circuit was measured. The current density was defined as the average value of the current that flowed when the short circuit occurred, divided by the area of ​​the metal foil.

[0084] (result) Table 1 lists the median diameter of oxide particles, the ratio of inorganic particles to oxide particles, the median diameter of inorganic particles, and the current density when short-circuited in the examples and comparative examples.

[0085] [Table 1]

[0086] The symmetrical cells in Examples 1-8 have a current density of 2.0 mA / cm² when short-circuited. 2 In contrast, the symmetrical cell in Comparative Example 1 had a current density of 0.5 mA / cm² when short-circuited. 2 It was found that the aggregates in Examples 1-8, in which inorganic particles are present between oxide particles, can achieve a higher current density during short circuits compared to the aggregate in Comparative Example 1, in which inorganic particles are absent. This revealed that the aggregates in Examples 1-8, in which inorganic particles are present between oxide particles, can reduce the growth of Li metal dendrites.

[0087] Although the aggregate in Example 2 was not a mixture of oxide particles and inorganic particles, it was possible to increase the current density during short circuits, similar to the aggregates in Examples 1 and 3-8, where oxide particles were mixed with inorganic particles. This revealed that aggregates formed when inorganic particles are generated during the preparation of oxide particles can reduce Li metal dendrite growth, similar to aggregates in which oxide particles are mixed with inorganic particles.

[0088] The symmetrical cell in Comparative Example 2 contains an aggregate of inorganic particles between oxide particles, but the current density when short-circuited is 0.1 mA / cm². 2 This was the case. Comparing Example 1-8 with Comparative Example 2, Comparative Example 2 differs from Example 1-8 in that the ratio of inorganic particles to oxide particles is large at 15 vol%. In Comparative Example 2, gaps are created between the oxide particles 19, so it is presumed that dendrites grew at the interface of the oxide particles 19, causing a short circuit.

[0089] The symmetrical cell in Comparative Example 3 also contains an aggregate of inorganic particles between oxide particles, but the current density when short-circuited is 0.5 mA / cm². 2 This was the case. Comparing Examples 1-8 with Comparative Example 3, Comparative Example 3 differs from Examples 1-8 in that the median diameter of the inorganic particles is larger at 3.0 μm. In Comparative Example 3, gaps also form between the oxide particles 19, so it is presumed that dendrites grew at the interface of the oxide particles 19, causing a short circuit.

[0090] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0091] In the embodiment, the energy storage device 11 was described as comprising a positive electrode layer 12 with an active material layer 14 provided on one side of a current collector layer 13, and a negative electrode layer 16 with an active material layer 18 provided on one side of a current collector layer 17, but it is not necessarily limited to this. For example, it is certainly possible to apply each element in the embodiment to an energy storage device comprising an electrode layer (so-called bipolar electrode) with an active material layer 14 and an active material layer 18 provided on both sides of the current collector layer 13, respectively. By alternately stacking bipolar electrodes and electrolyte layers 15 and housing them in a case (not shown), a so-called bipolar structure energy storage device can be obtained.

[0092] In the first embodiment, the case in which the active material layers 14, 18 and the electrolyte layer 15 all contain aggregate 10 was described, but the invention is not necessarily limited to this. The energy storage device 11 only needs to have at least one of the active material layers 14, 18 and the electrolyte layer 15 contain aggregate 10.

[0093] In the second embodiment, the case in which both active material layers 14 and 18 contain aggregate 10 was described, but the invention is not necessarily limited to this. The energy storage device 24 only needs to have at least one of the active material layers 14 and 18 contain aggregate 10.

[0094] In the third embodiment, a protective layer 29 is described as being present between the active material layer 31 and the separator 25, and a protective layer 32 is present between the current collector layer 17 and the active material layer 31. However, the embodiment is not necessarily limited to this. It is naturally possible to omit either the protective layer 29 or 32.

[0095] In the embodiment described, the case in which the aggregate 10 includes the electrolyte 23 was explained, but it is not necessarily limited to this. It is certainly possible to omit the electrolyte 23.

[0096] In the embodiments described, the case in which the active material layers 14, 18, electrolyte layer 15, and protective layers 29, 32 (sheets) are made using the aggregate 10 has been described, but the invention is not necessarily limited to this. The aggregate 10 is a collection of many objects, and includes all of which are traded as a single object. Other forms of the aggregate 10 include a mixture of oxide particles 19 and inorganic particles 22, a mixture of oxide particles 19 and inorganic particles 22 with an electrolyte 23, and a press-molded body of a mixture containing oxide particles 19 and inorganic particles 22.

[0097] In the embodiments, lithium-ion batteries were used as examples to describe the energy storage devices 11, 24, and 26 that include the aggregate 10, but the invention is not necessarily limited to these. Other energy storage devices that include the aggregate 10 include lithium-ion capacitors, lithium-sulfur batteries, lithium-oxygen batteries, lithium-air batteries, and the like. [Explanation of Symbols]

[0098] 10 Assemblage 11, 24, 26 Energy storage devices 12. Positive electrode layer (sheet, electrode) 15. Electrolyte layer (sheet, separator) 16. Negative electrode layer (sheet, electrode) 19 Oxide particles 22 Inorganic particles 23 Electrolyte 25 Separators 29,32 Protective layer 36,38 electrode

Claims

1. An aggregate containing oxide particles having a garnet-type crystal structure including Li, La, and Zr, used in energy storage devices, It consists of typical elements and further contains inorganic particles including Mg, The median diameter of the inorganic particles is 1 / 2 or less of the median diameter of the oxide particles. An aggregate in which the ratio of inorganic particles to oxide particles is 1 vol% or more and 10 vol% or less.

2. The aggregate according to claim 1, further comprising an electrolyte.

3. A sheet comprising the aggregate described in claim 1 or 2.

4. An electrode comprising the aggregate described in claim 1 or 2.

5. A separator comprising the aggregate described in claim 1 or 2.

6. The protective layer comprises the aggregate described in claim 1 or 2, and the electrode is in contact with the protective layer.

7. A separator comprising the aggregate described in claim 1 or 2, wherein the protective layer is in contact with the protective layer.

8. An energy storage device comprising the electrode described in claim 4, wherein lithium ions are used as carriers.

9. An energy storage device comprising the separator described in claim 5 and using lithium ions as a carrier.

10. An energy storage device comprising the electrode described in claim 6, wherein lithium ions are used as carriers.

11. An energy storage device comprising the separator described in claim 7 and using lithium ions as a carrier.

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